Lets say that we have two guns, they both fire the same bullet,

>>35167583
The one without the sabot because the sabot is added weight needing to be propelled down the barrel

Depends on the length of the barrel.

A larger diameter with a given powder charge will be better suited to a shorter barrel but you'll eventually reach a point where the added friction cancels out the gain in peak pressure

>>35167606
Oh yeah i guess i should have addressed that in my post, lets assume that the sabot has no mass and that it produces the same amount of friction as the bullet traveling down the smaller caliber barrel.

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The sabot adds negligible weight usually compared to the payload. The increased surface area on the base of the projectile+sabot increased the force that impinges on the projectile, hence the top one will accelerate more quickly. Additionally, most apds/apfsds contact the walls of barrel far less than a traditional spitzer projectile.

The bullet's resistance in the bore would be the deciding factor. I don't know which way it would push it but that's the only significant difference.

>>35167606
Sabots weigh practically nothing.
The bullet's resistance in the bore would be the deciding factor. I don't know which way it would push it but that's the only significant difference. The only other thing

>>35167634
Well now that you add all that shit what's the point of the question in the first place? You're asking a physics question and trying to take half of the physics out of it.

>>35167681
>Sabots weigh practically nothing.
They still weigh something so depending on how technical we get or precise we would be measuring, the sabot would be slower.

>>35167681
So basically the only difference would be the difference in friction created by the different projectiles? What if you selected the different projectiles materials so that they both create the same amount of friction, would that mean that they would have the same muzzle velocity?

>>35167757
Well yeah but that's so obvious that it's boring, how about we focus the discussion on some other aspects that one might not be able to realize at first.

>>35167583
It depends on the burn rate of the propellent, faster burn rate would favor the sabot as it would empart more energy on to the projectile in a shorter time, slower burn rate would favor the bottleneck.

>>35167760
If the sabot is weightless and the friction of both projectiles is the same then the top one will accelerate quicker.

Pressure = Force/Area

So for the same peak pressure generated by the powder, a larger area at the base of the projectile will increase the force acting on the round.

Force = Mass x Acceleration

So if the force acting on the base of the round is larger, a projectile of the same mass will accelerate faster, assuming the friction on the inside of the barrel is the same.

>>35167757
The sabots lower resistance through the barrel would have a much larger effect than the negligible weight increase.

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>>35167606

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>>35167634

>lets assume that the sabot has no mass

Is rather assume something plausible, like your cock addiction.

>>35167823
Interesting, really makes you wonder why they bothered to develop a small bore short barreled weapons like the Five-Seven and the P90, i mean why not just use saboted 9mm or something? Although i guess you would be wasting energy due to having to have a sabot.

>>35167904
>>35167900
>>35167757
How about we just talk about muzzle energy instead of muzzle velocity then? This way the marginal weight of the sabot will not matter in this discussion.

>>35167917
Smaller caliber projectiles need a lower shear force to punch through armor, hence why they chose to use smaller caliber rounds for CRISAT. The overall energy levels of 5.7 and 4.6 are less than 9mm but 9mm has a harder time breaching Soviet soft body armor.

>>35167958
Yes yes, that's why i suggested saboted 9mm.

>>35167939
Depends on the length of the barrel being used. Think of a rifle's barrel as a pressure vessel that continually increases in volume as the bullet travels down the barrel. A wider barrel with a bullet using a sabot will reach a certain volume quicker than a thinner barrel firing a non saboted bullet. Therefore the sabot rifle will accelerate more quickly in a shorter amount of time, but the friction force of the sabot on the barrel walls will exceed the expansion force of the powder more quickly and in a shorter distance in the barrel.

>>35167958
Explain 7.62x25 then faggot

>>35167968
A saboted 9mm would be a very large projectile and would require a very large gun and would be required to use a lower capacity magazine. The sabot would also have to be comparatively wide in order to generate sufficient energy to give a 9mm round enough energy to penetrate body armour.

>>35167823
by your math the pressure would be lower, if the applied energy is the same so the higher area would lower the pressure. I think it would be analogous to a garden hose

>>35168029
Explain what about it?

>>35168050
Why would the pressure be lower; you have the same amount of powder?

>>35168040
No wait, i meant that the sabot would be 9mm across and the bullet itself would be smaller to facilitate penetrating body armor easier. That way you might not have to get new guns, just new ammo, sorry if i worded it poorly.

>>35168059
I'm not him but wouldn't the same amount of powder and a bigger container mean that the pressure is lower.

>>35168051
How's a 30 caliber round gonna rekk harder than the 5.7?

But but how did plane upside down fly?
>>>/sci/

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>>35168106
That's basically what the 6.5mm CBJ was, and yes it would have been sick if America (and hence NATO) wasn't so adamantly gay about it's logistics.

>>35167677
This is the correct answer.

>>35168117
One sec lemme MS Paint ninja this shit real quick

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>>35168158
Don't fall for the Swedish snake oil rounds.

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>>35168117
Basically in order to match the same level of energy being imparted to a 9mm by the burning powder, the 5.7mm has to travel further than a 9mm would and therefore the barrel has to be longer. This is offset by the lower weight of the 5/7mm projectile which will accelerate quicker. However, you can look at 5.7mm 5" barrel muzzle vels vs 9mm 4" barrel muzzle vels and see that the 9mm clearly has a muzzle energy advantage, indicating that the 5.7mm requires and even longer barrel than 5" to even get close to the 9mm in terms of muzzle energy.

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>>35168262
If the barrels have the same volume does that mean that the muzzle energy will be the same? If so, man high caliber saboted guns are fucking awesome no wonder they use em on tanks and such.

>>35167757
>>35167681
OP could have said that the mass of the sabot and saboted bullet equals the mass of the unsaboted bullet

>>35168296
Yeah that would have been one way to avoid the issue of people latching on to irrelevant stuff.

>>35168059
The barrel is wider because of the sabot, so you have the same amount of gas occupying a larger volume.

>>35167583

If your propellant can provide similar pressure for both barrels even though other has dramatically more ΔV than the other. Naturally the saboted one will gain more velocity because F=P*A right?

>>35168283
The only reason why saboted guns aren't really used is because any bullet that can be considered "man portable" i.e. 7.62mm is still too small to effectively sabot because the case is so large. Let's say you have a 308 cartridge with a 4mm saboted projectile. In order for that projectile to approximate the same weight as normal m80 ball round, the bullet would have to be very long compared to their diameter (oversquare) and therefore impossible to spin stabilise; hence why all modern armour piercing tank rounds are fin stabilised. This carries the issues of the weight of using a full power rifle cartridge, the terminal effectiveness of the projectile on soft tissue (if tungsten is used it's armour penetration probably exceeds what is actually required i.e. NIJ level 3 plates), it's ability to penetrate brush effectively and finally it's cost and feed reliability.

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>>35168373
>any bullet that can be considered "man portable" i.e. 7.62mm is still too small to effectively sabot because the case is so large

Sorry for my retardation, I meant to say that the case neck is too small.

>>35168373
It is incredibly interesting (to me atleast) how all the intricacies of the universe translate into firearms design, i juat can't get enough of it.

>>35168336
The pressure will change over time as the propellant burns and the bullet moves along the barrel. The wider barrel will have the same volume as the thinner barrel, but in a shorter distance. The pressure will drop off quicker from peak pressure in the wider barrel and hence you will get diminishing returns much quicker from a wider barrel than a thinner one.

>>35167583

Bottom one has higher muzzle velocity.

t. Bernoulli

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>>35168699
>Bernoulli
I don't think that equation means what you think it means.

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>>35168728

Both powder charges burn at the same rate, but one is forced into a smaller opening, meaning that the velocity must be higher. Unless I am retards and am missing something huge here.

I have a physics degree, I should really be able to explain this whole thing but it's 1am and I'm about to have a wank

>>35168844
I can see why you'd have that misconception but that doesn't describe the rate at which the projectile picks up speed, only the rate at which the gases would flow from one area to another downstream and not in a sealed pressure vessel like a gun barrel.

>>35168868
Pls UKanon

>>35168144
Because lift is being generated and either the plane has to maintain a higher angle of attack to maintain lift or the curvature of the wings of the plane is symmetrical so the only thing different between normal and upside down flight is the orientation of the pilot and landing gear.

I'm just a simple man but the bottom one has a smaller surface area to disperse the pressure upon so should it be a higher presssure than the above one which has a greater surface area on which to impart pressure

>>35168951
I assumed flying upside has more to do with thrust than lift.

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>>35168117
Came here to say this.

>>35169252
Pressure acts unilaterally on the inner wall of the case as a result of the deflagration of the powder. With a necked case, the pressure will act on the shoulder of the inside of the case as opposed to what would have been the base of a saboted projectile. As long as the inner case volume and powder charge are the same in both rounds, the initial pressure will be the same in both rounds.

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>>35169514
Forgot pic

>>35167583
Larger bores are more efficient, so the the top one.

>>35167823
Do you mean friction or friction coefficient, because those are very different things. If the bullet and the sabot have the same coefficient, the sabot would be slower because it have a wider diameter and thus a higher surface area of contact with the barrel.

2. Are you a fucking retard? A larger base would decrease the pressure (not by any amount that would matter) not increase it. is 1/4 bigger than 1/2? No, when you divide by a bigger number you get a smaller fraction dumbass

>>35169659
Friction is determined by the coefficient of friction constant (static or kinetic) and the normal force between the two surfaces. Area of contact surface does not contribute.

>>35167583
Someone with a .243 and .308 should test this. I would, but I can't be bothered to use up any of my sabots.

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>>35169659
I said friction and I meant friction because if both have the same friction force acting on them then friction can be ruled out as a factor.

Pressure has to remain the same in both cases at ignition because both have the same propellant in the same quantity. The surface area of the base of the projectile has increased and as a result the force on the base of the projectile has also increased; it must do because we know that pressure in the chamber is the same in both examples. So no it's not like 1/2 changing to 1/4, it's like 2/2 changing to 4/4.

Dumbass.

>>35167583
With the same amount of powder, the same volume of gas would be produced by a burn of the same efficiency. Pressure is inversely related to pressure vessel volume (PV=nRT) therefore the larger bore will have lower pressure acting on the bullet base.

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>>35169942
Pressure acts uniformally on the walls of a pressure vessel so why would the pressure on the wide base be less than on the narrow base if the cartridge interior dimensions are the same?

>>35168117
>I'm not him but wouldn't the same amount of powder and a bigger container mean that the pressure is lower.

Force = Pressure x Area
>do you even pascal?
Also, there is some atomization that occurs in the early stages of an explosion, some slow burning powders will actually cumbust with more pressure when they have more headspace

>>35170120
>Pressure acts uniformally on the walls of a pressure vessel so why would the pressure on the wide base be less than on the narrow base if the cartridge interior dimensions are the same?


t. Blaise Pascal

>>35169906
See >>35169942 as to why pressure would not end the same. For the same amount of gas produced by the powder, temperature, and same length of barrel, pressure will be 1/4 smaller in the larger barrel

>>35169659
For simplicity's sake we will say the smaller bullet is 1/2 the diameter of the large projectile, D.

Rearranging the equation of pressure for force, we get F=P*A. For the larger bullet, F_l=P*(pi*D^2/4). For the smaller projectile: F_s=P*(pi*(D/2)^2/4). Simplifying, this becomes F_s=P*(pi*D^2/16). Setting P*(pi*D^2) equal to itself, we get 4*F_l=16*F_s. Dividing both sides by 4 we arrive at F_L=4*F_s. So force acting on the large projectile will be 4 times larger than on the small projectile.

Combining the two things above we reach the conclusion that the will have the same force acting upon them. The difference will then be because of the location of the pressure spike with relation to time and inherent efficiencies of cartridge geometry.

>>35170120
See the above info. Pressure acting on the bullet base will be lower, but the force will bend up being the same.

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>>35170182
I should add that I figured pressure will be 1/4 smaller in the large barrel for same number of mols gas assumed that the smaller barrel was 1/2 the diameter of the larger barrel and there is no rifling because figuring rifling volume out would be too complicated not to do on paper.

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This is a graph of Pressure vs Volume (Boyle's law), Pressure vs Time (Sabot projectile, PT1) and Pressure vs Time (Spitzer projectile, PT2). Because of the increased force on the base of the saboted projectile, it will reach its friction slip limit earlier than the Spitzer projectile. Because of this, the Spitzer projectile will have a higher peak pressure as the propellant gases have longer to expand before the bullet starts to slip but the saboted projectile reaches its peak pressure sooner.

Sorry for yet more shit phone MS Paint

>>35170182
I was only talking about the projectiles before they slip btw, I'm >>35170323

>>35169514
No, I was thinking of what happens when the projectile starts moving. >>35167677 said the projectile accelerates more quickly

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>>35171038
They don't accelerate differently. See pic related. Since op said earlier in
>>35167634 that their Frictions are the same, there will be no difference in velocity vs time graphs between the two.

>>35167583
What? The point of a sabot is to protect the more sensitive payload when using more propellant than the payload can handle.

>>35171285
You're assuming the chamber is the same diameter as the bore in both conditions. In OP's image it looks like the chambers are about the same size, with one being necked down to a small barrel.
If the chambers are identical in volume, discounting burn efficiencies and rates etc, the pressure at the base of the projectile will be the same and the initial acceleration will therefore be higher for the larger diameter projectile. The pressure will drop off more rapidly for the larger diameter projectile.

>>35171495
While nothing you said is wrong, I still think they'll have the same pressure spike, just translated linearly from one another in regards to time. With a long enough barrel, they will yield the same muzzle velocity. Inherent efficiencies of the chambers matter, too, but we can't really make much sense of the given problem because we have incomplete information in the cartridge geometry and barrel length

A larger bore diameter would need more powder or a slower burning powder to get the same velocity of the smaller bore. In a smaller bore there is less space, whereas the larger bore has more capacity to take up so in turn would have to have a slower burning powder to accelerate the bullet or sabot at the same rate as the faster burning powder as the smaller bore. There will be more pressure in the smaller bore

>>35171640
Yes, if you had frictionless adiabatic barrels of infinite length, such that the pressure behind the projectile can eventually drop to 0, the projectiles will achieve the same velocity. You don't even have to do the math on it, you know that if you start with identical chemical energies and put all that energy into a projectile then you'll get the same energy in the projectile, and if the projectiles weigh the same then they'll have the same velocity.

If the barrels are the same (non-infinite) length, but still frictionless and adiabatic, the sabot will achieve a higher velocity as at any given distance as it will have absorbed more energy thanks to its larger area (and resulting pressure curve which drops off more rapidly).

>>35171886
I'm interested in how this would shape up real world. I know 7.62 to 6 mm sabots exist, I wonder if anyone has bothered shooting the same bullet in a .243 and .308 Winchester with the same powder charge

>>35171978
You'll get a higher velocity from the 243 than you will out of a 308 rifle with the same length barrel. In order to get the same muzzle energy as the 308, the 243 rifle will need a longer barrel than the 308 rifle.

>>35167583
Smaller barrel. Because the same ammount of energy has less space and area (the back of the bullet) thus creating more pressure and giving it higher velocity

Good job OP, that's a fantastic clusterfuck of actual physics and fuddlore you've constructed in here.

>>35167958
Why not just have all your ammo be hot hardened steel core ammo then? Why develop a new Cartridge?

>>35173856
Hardened steel is less dense than lead and hence for the same size of bullet, the sectional density will be worse. This means that the bullet retains kinetic energy worse over distance due to air resistance.

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Bottom one is clearly faster if you scale it up

>>35167634
So, what you're asking is, "Would the increased volume of the bore produce a lower final velocity?"

>>35173708

Wrong.

Same gunpowder = same pressure.
Pressure = Force/Area
Area of Bullet < Area of Bullet+Sabot
More Area = More Force = Bigger Muzzle Velocity

That's why all dedicated armour piercing rounds since WW2 are saboted: it gives the round higher muzzle velocity, and hence, more kinetic energy.

>>35173876
No, it isn't. Think of it as how hard you have to blow through a pea shooter to fire the pea at a certain speed. If you use a wider tube that fires the same weight projectile you will not have to blow as hard to fire the pea at the same speed as in the other tube.

>>35173907
same volume of gas is produced
Smaller barrel has less volume so higher pressure, so round goes faster..

basic science..

>>35173907
In addition to the rounds requiring a lower shear force to penetrate (because they're narrower), having a higher sectional density (better wind resistance) and the ability to maintain high velocity when using non-steel hardened materials, like tungsten.

>>35168392
Uh, .30 sabots for loading 5.56 projectiles is a thing.

>>35173928
They aren't accurate though

>>35173702
To a point, barrel length eventually results in diminishing returns. And even negative if you start to get a bit crazy long with it.
Plus powder selection would be a huge variable.

>>35173907
Yeah...
This is wrong.
And you should feel bad.
Just a lil

>>35173912
So science. Much maths.
WOW

>>35173943
Bullets are really only losing velocity in the barrel after 50 inches plus of barrel length, but yes obviously you get rapidly diminishing returns after about 28". However, some cartridges, such as the 6.5 Grendel, can leverage more use out of extra barrel length and if longer barrels are used, these cartridges can be very very energy efficient when all things are considered.

>>35173867
Yes and it will still have better penetrating ability.
Also you could add a boat tail to increase fluid travel efficiency or have a hardened steel penetrator tip and the rest hard cast lead.

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>>35173876
after firing, gas has expanded to 3 times the volume of the gunpowder.

2 is clearly winning

>>35173900

>Ding ding ding
>/thread.
Op is asking a very simple physics problem about two cylinders, one with a larger volume, asking which would fill faster.

>>35173960
Anon I don't know what to tell you; I genuinely think you're retarded.

t. mechanical engineer and competition shooting for 8 years

>>35167634
If the sabot has no mass and the same friction then the bullet, then the sabot will zip off down the barrel while the bullet is accelerating.

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Ok, this shit is all retarded so I'm going to have to make myself very clear so we're no talking across purposes.

Let's for a moment talk about the bullet, seated in the case, ASSUMING FOR SIMPLICITY'S SAKE THAT THE BULLET HASN'T SLIPPED OR MOVED so that we are measuring the pressure inside a fixed pressure vessel after primer ignition.

Pressure is defined by the force of random collisions of particles inside a container dispersed over a certain area, hence:

Pressure = Force/Area

At peak pressure, if you were to measure the pressure at any point on the inside of the case wall or over any particular area the pressure WILL ALWAYS BE THE SAME NO MATTER WHERE IT IS MEASURED because pressure acts UNIFORMALLY. The pressure is a constant in the equation; the Area is our control value because we're changing how much of it we measure and the Force is our variable or measured value.

So therefore, we know that the pressure in the container has to stay the same and we are increasing the area we are measuring (small bore --> large bore), so in order for pressure to remain constant THE FORCE ACTING OVER THE AREA MUST ALSO INCREASE to compensate for the increased surface area.

This means that before the projectiles start to move, the larger bore will be providing more force to the saboted projectile than the thinner weakshit spitzer because it has a wider base.

Now, about what happens when the bullet overcomes friction and starts to slip down the barrel.

We already know that the Acceleration of a projectile is defined by Accel=Force/Mass and from another anon that Total Friction Force, Fr, is independent of contact area and is defined by Fr = μR where μ is the friction coefficient and R is the reaction force of the bullet pushing against the lands of the rifling.

Let's for a moment assume that the Fr for both projectiles is exactly the same so they both require the same amount of force to get moving. In this instance, the force, Fr, is our constant... (1/2)

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>>35174116
...and we are changing the area, A, of the base of the projectiles to find the pressure required to get the projectile moving.

Let's say the area of the saboted projectile's base is twice as large as the non-saboted projectile. The two equations look something like this:

Pressure = Friction/Area of bullet base

So for a non-saboted projectile the equation is P = Fr/A but the saboted projectile has double the base area so we know that it requires half as much pressure for the saboted projectile to overcome the same amount of friction force i.e P/2 = Fr/2A

This means that when we look at the expansion-time curve of the propellant, the saboted projectile has already started moving whilst the non-saboted projectile is still in it's case, waiting for the gas to build up enough pressure to allow the bullet to overcome Fr. This is why the non-saboted projectile has a higher PEAK pressure than the saboted projectile.

Since the masses of the projectiles are both the same (sabot weight is negligent) and we know that Acceleration = Force/Mass, the saboted projectile initially has a higher force doing work at the base of the projectile so it will accelerate more quickly than the saboted projectile. However, as the pressure vessel increases in size more quickly with respect to length in the saboted barrel due to the wider bore, the expanding gases will impart most of their energy earlier on and so there will be greatly diminishing returns when using a longer barrel.

Assuming the barrels had infinite length, they would impart the same amount of energy to both projectiles because the amount of propellant in the both cases is the same. However, the non-saboted projectile would go further in distance ,albeit slower and not as far as you would think. Don't forget; the non-saboted projectile needs twice as much pressure as the saboted one to overcome the friction in the barrel. (2/2)

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conventional projectiles a shit

ive read this whole thread and not a single anon has brought up the high-low system

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>>35167583
Sabot will travel farther with less drag because of less surface contact while acting as the gas stopper before the penetrator exits.

>>35173978
Except it's not, dumbass. There's a whole host of other factors.

>>35174116
My god, you're a total imbecile, and you're truly proud of your imbecility.
OK let's put it as simple as possible so that even someone like you could understand it: the powder doesn't burn instantly, and the gases don't flow effortlessly out of the cartridge. The moment the powder is ignited the pressure will start to build up; when a certain point is reached, usually when about of quarter of the powder has already burned, the bullet will start moving. Because of the smaller bullet the hole thru which the gases have to come out and the barrel diameter after that is smaller so the volume in which it expands is a lot smaller the pressure inside the cartridge will rise far higher; this in turn will put far more accelerating force behind the smaller bullet and will stay like that for far longer. In the end the smaller bullet will have a noticeably higher speed and energy than the saboted round.
Got it, you absolute cretin?

>>35174520
>t. know nothing retard

It's literally simple piston physics; you do this shit in year fucking 1 of college; you did go to college right? How do you not understand how this works? Why do you think F1 engines use massively oversquared pistons with short throws? It's so that the pistons can accelerate and decelerate quicker to get higher angular velocity at the crank.

>Because of the smaller bullet the hole thru which the gases have to come out and the barrel diameter after that is smaller so the volume in which it expands is a lot smaller the pressure inside the cartridge will rise far higher

The volume the gas has expanded to correlates with the amount of energy it has transferred to the projectile + rifle (Newton's third law, no way you can deny that unless you're deliberately being retarded), hence as long as the volume of gas in the system is the same, the wider bore will have transferred the same amount of energy as the smaller bore as but in a shorter distance. This indicates it has accelerated quicker.

>In the end the smaller bullet will have a noticeably higher speed and energy than the saboted round.

No mention of barrel length.

THINK. Maybe next time your opinion won't be as shit as your grammar.

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If only somebody made a device to measure the velocity of a bullet we could actually test this....
Oh they do, if you load a 308 with a 200gr bullet and a 200gr bullet in a .358 win, with the same powder, the 308 will achieve 2400fps with 41 grains (max load), and with the minimum load of 44grains the 358 will reach roughly 2300fps,

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>>35174699
And the .358 data

>>35174699
>>35174708
Ok, now show what velocities you get if you cut the barrels down by 10"

Listen, nobody is saying that you're going to get faster velocities out of sabot ammunition in literally every occasion, only that the wider base causes it to accelerate more quickly. There's a reason why 300BLK only really needs a 9" barrel to match 14.5" 5.56mm barrel energy levels.

Also,

>with the same powder
>41 grains, case capacity 56gr
>44 grains, case capacity 57gr

They're similar but the example isn't perfect.

>>35174769
Fair point on the imperfect example, however The 300blk is also using a much heavier bullet and faster powder to get those energy results, and it is getting them at a lower velocity,

>>35174799
I think most examples of this are going to be somewhat imperfect because of a whole host of other factors.

>Throat length
>Twist rate
>Cartridge neck length
>Cartridge void space

The best experiment would be between 2 smoothbore sabot guns like a 105mm L/52 and a 120mm L/44 with the same projectile weight.

>>35174618
Oh, i see it now, you got your college diploma from Bubba's Bible College and Bait Shop, they never bothered explaining to you what fluid dynamics is and how it works.
So, since you never learned that, the reason they use oversquare pistons in high revving engines is not for the possible higher torque as you so idiotically believe but for a much faster fluid exchange in the cylinder. In fact the severely oversquare engines like those of F1 have significantly smaller torque than normal ones of the same capacity, they get their power from the much higher revs not the force pushing on the much larger pistons.
And no, that's the point here, the amount of gases doesn't stay the same, it actually grows as the powder burns and that happens as the bullet is already travelling thru the barrel. In fact in most handheld weapons not all power is burned by the time the bullet is out of it. So no, the length of the barrel doesn't matter that much on the final speeds, the saboted round will always have a much lower speed and the difference will only grow as the barrel gets longer.
Go back to humping your sister you idiotic inbred, leave science for those with an IQ higher than your hourly wages.

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>>35174863
>>>(you)

>the reason they use oversquare pistons in high revving engines is not for the possible higher torque as you so idiotically believe but for a much faster fluid exchange in the cylinder

Firstly, I didn't mention torque anywhere in my post (and even then your niggerbait totally ignores that the low torque is a result of the short crank throw rather than the combustion cycle), so not only can you not spell the word "through" properly or into mechanics, you also apparently can't fucking read either.

>And no, that's the point here, the amount of gases doesn't stay the same, it actually grows as the powder burns and that happens as the bullet is already travelling thru the barrel

Literally not even worth replying to; there's a whole spiel above indicating why you are wrong.

>In fact in most handheld weapons not all power is burned by the time the bullet is out of it.

You are 10000000% fucking percent retarded. In every single functioning firearm on this planet, the powder will be entirely burned within 3" of the chamber throat.

>>>>>>You need to be 18 to post on this website.

>>35174959
>In every single functioning firearm on this planet, the powder will be entirely burned within 3" of the chamber throat.
And now i know that you never fired a gun in your life and are only larping.
Bye, loser.

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>>35174988
ok loser

>>35167583
my first intuition is the sabot, as the hot gas in the chamber has a greater area to act on
F = P/A after all
but near the end of the barrel, the same gas has to fill a markedly larger volume. I don't know quite how to consider that.
I do know that most of the velocity of a projectile is ~logarithmic with respect to barrel length, so i don't think the volume increase should be enough of an issue.

final answer: sabot.

>>35167677
The first half is wrong. Keeping propellant the same for both, the force in both is then identical. What changes is the surface area of the projectile, as you identified. Force applied over an area is measured as pressure(P=F/A). Keeping force the same, a higher pressure can only result from a reduction in surface area. This implies the lower example would go faster in a frictionless system.

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>>35167583

Sabot would be slower because lower pressure

>>35169514
The pressure will be the same, but force is pressure acting on an area.
a greater area means a greater force

>>35175076
P=F/A

Pounds per square inch -> lb./in^2

>>35175041
woops made an algebra mistake
F = PA
obviously

>>35175097
yes and?

>>35175117
And you're a moron. Force is not pressure acting on an area. It's the reverse. A greater area necessitates a greater force to maintain pressure.

>>35175196
brainlet. i'm not going to address this shit stain of a post.
think about what you said

>>35175205
Here you go bud, get your dictionary out and learn something

>>35175226
https://en.m.wikipedia.org/wiki/Pressure

>>35175196
I think you just worded that kinda poorly

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here you go, Dunning-Kruger

Basically, using a sabot doesn't magically net you any total gains, it just allows you to get better efficiency out of a short barrel; especially useful in large bore tank barrels where they have to operate innacity and can't afford to be swinging around a 20 metre long barrel.

>>35167583
Every since I found out I can buy saboted bullets in calibers smaller than .30, I've been considering reloading some .30-06 brass with them and playing with them in my durr rifle.

>>35167606
Although that would still be a very minor issue. Most Sabots weigh as close to nothing as they can make them precisely because of what you said.

>>35167583
-Assuming the burn rate is the same, Force will remain constant: F=M*A, M=mass of powder and A=acceleration of powder as it expands outward
- P=F/Area, P*Area=F
- As A decreases, P must increase to maintain F
- Volumetric expansion for the powder in both cases will remain the same, but the direction of said expansion will vary.
- The lower barrel will produce a higher muzzle velocity as the lateral volumetric expansion will be faster.

Many in this thread are confused as to why the lower is faster. That is because they believe P to be the same, when F is the constant. P and A are variable.

So, why are high velocity guns almost always APFSDS? Simple, quality steel/gun barrel material can only contain so much pressure before failure. To reduce the weight of the gun, they increase the bore diameter and either use more propellant or a faster burning propellant to reach standard pressure. Now P is the constant and F will increase to overcome a larger A, producing larger muzzle velocity per barrel length. Also, a saboted round will have a higher sectional density and perform better after propulsion while maintaining the low pressure high force gun dynamic.

>>35175634
it's erroneous to assume pressure changes and not force.
pressure is a function of temperature, number and volume for a gas NOT force

>>35175656
No, this is a simple example with the same powder, volume of powder, burn rate temperature, etc. The force produced by the powder in OPs example is constant. With every change in bore area will come a change in Pressure.

Reread my post. I'm correct.

>>35175688
>The force produced by the powder in OPs example is constant
you have a gross misunderstanding of what "force" and "pressure" are

>>35175751
No. No I don't. I've been an aerospace engineer for 6 years now. I know what I'm talking about jackass.

>>35175751
Semantics lmao

He said force and you know he basically meant force (per unit area) i.e. pressure and yet instead of adding anything to the discussion you made this post.

>>35175751
>>35175768
Btw, a real life example includes both the pressure and force exerted on the barrel/bullet vary. But this was a simplified example to explain why the smaller bore will produce a higher muzzle velocity with the given constraints.

>>35175768
>>35175777
Both instances would have the same chamber pressure at t=0.
both pressures would be acting on different sized areas. those differences in area would create a difference in force experiences at t=0.
the pressure would drop off faster for the larger area, than for the smaller one.
that leaves a small time interval where the larger area barrel would have greater force acting on the bullet.

see >>35175287
if you're an engineer, you're a piss poor one.

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>>35175634
The lower sized barrel will be slower not faster. At every point in the barrel up to the muzzle the acceleration of the sabot will larger than that of the smaller projectile, meaning the velocity of the sabotage, too, is larger.

>>35167583
Alright you brainlets, listen up. Simple physics dictates that the pressure on the bottom barrel would be much higher because of the reduced area in which the bullet/propellant must travel through.

Pay attention in high school next time anon.

LA = large area if top muzzle
SA = small area of bottom muzzle
A = normalized area unit for this demonstration

Let's assume
LA = 2A
SA = A

Pressure = F/A

Assuming F is constant since the same amount of propellant is used in both situations

Sabot pressure = F/LA = F/(2A)
Non-sabot pressure = F/SA = F/A

Pressure is obviously higher without the sabot, meaning muzzle velocity is higher without the sabot assuming the sabot provides identical barrel friction as the bullet and is weightless.

>>35175777
>He said force and you know he basically meant force (per unit area)
You know there's a word for force (per unit area), it's usually referred to as "pressure".
The more you know.

>>35175819
You know how to write equations like that yet you are so retarded. Your teachers would be ashamed.

>>35175913
see >>35175287
you're making meaningless assumptions that don't justify your claim, and you're making additional assumptions that you don't disclose

>>35175925
Nice refutation

There is some barrel length where both projectiles will exit with equal speed.
At lengths shorter than this, the large barrel will yield a faster projectile.
At lengths longer than this, the small barrel will yield a faster projectile.

There is nothing more than can be determined without actually knowing all the specifics of the situation, which we won't ever know because OP just made this up.

>>35175934
The picture proves my point you retard. Higher volume (barrel radius) means lower pressure (muzzle velocity).

>>35175951
and what tell would happen if the barrel were short?
that distance the pressure is higher isn't relegated to picometers, brainlet

>>35175956
>pressure is higher
sorry, i meant force

>>35175816
>>35175819
Retards
>>35175913
Correct
>>35175956
It would still have a higher velocity

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>>35175988
>It would still have a higher velocity
do you know what the integral of force over distance is? obviously not
it's energy. do you know what is proportional to energy? speed.

in pic related we can see an obvious example of where a larger barrel would yield a higher energy for the projectile.
guess what that higher energy means.
i know you can do it if you tried
you seem like the kind of kid who would say they're "smart but lazy."
don't be so lazy

>>35175947
You solved for F using a constant P. That immediately trashes the rest of the equation.

F is the constant here, which you are using to solve for P.

You are basically saying for a given pressure, the larger area creates a larger force. The force is the given, not the pressure.

>>35176038
>F is the constant here
wrong.
if F were constant, both masses would have the same acceleration
F = m a
obviously they don't, so force is not constant.

>>35176038
P isn't constant. Its determined by volume of the pressure vessel, the number of moles, gas constant, and temperature (the last three of which are constant for any given time). The initial pressure is a constant and only represents chamber pressure before either bullet has overcome its static friction. Since pressures are scalar, the can just be added as more pressure is added from expanding gasses. Pressure varies with diameter and barrel length in the equations, as does force, and acceleration

>>35176027
That's not what I'm saying. I'm saying the force exerted by the same load of powder is... the same! Wow, who would've guessed!

So is the rate of volumetric expansion. So, the same amount of gas will push a bullet farther along the barrel faster if the barrel has less volume.

I'll leave it at this and let you ponder your posts. I have to get back to work.

>>35176104
you don't understand what "pressure" and "force" are

>>35176027
Brainlet with english degree trying to act smart.

Simplified, Work = Force x Distance (W = F x D), meaning the distance in which the projectile is under a CONSTANT (or defined) force, meaning shorter barrel = less time under force. Do you understand that when the bullet leaves the barrel, it is no longer under the influence for the force propelling it?

A longer barrel yields higher muzzle velocity because the bullet is subject to force for a longer time. If the barrel is a larger diameter, the force is smaller because the area is larger (P = F/A).

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>>35176125
I'm a PhD candidate in physics.
you have an extremely myopic perspective on the physical reality of this situation and you're making a lot of erroneous assumptions

fuck off back to /v/ or wherever your dunning-kruger ass came from

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>>35176125
Post credentials (and guns)

>>35176148
Obviously from a low tier liberal arts college if you think a larger diameter barrel results in a higher muzzle velocity from the same load of gunpowder with the same projectile mass. I am an engineer, so I actually make things for a living, not sucking off my advisor for good boy points.

>>35176181
It won't have a lower force you absolute nonce.
at the end of the barrel it will undoubtably have a lower PRESSURE, but guess what if the area on the back of the projectile is large enough, the FORCE (Pressure * Area) will be higher.

now hurry up and fuck off back to your daycare

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>>35176181
Dude you can't make this assertion whilst still omitting the massive elephant in the room that this situation is totally dependant on barrel length.

>>35176165
from his earlier posts it's clear he's still in high school

>>35176207
Prims but no tort ammy. Dh top and bottom. Untrimmed strength. Playing a male (male) character. Absolutely disgusting.

>>35167904
assuming something is massless can be completely valid...

>>35176181
Yet apparently not a very good engineer

I really hope you guys arguing the smaller barrel is faster with "science degrees" are just baitposting and not this legitimately ill-informed. The only actual thought out and demonstrated evidence has pointed to the sabot having a greater velocity for any barrel length where acceleration remains positive. Everything else has been conjecture and misguided thoughts

>>35168345
correct answer

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>>35176268
>tfw engineers are the brightest minds in their country
>tfw their country is fucked

Engineers <<<<< "Liberal Arts"
(all of the Sciences and Mathematics are "Liberal Arts" )

>>35171285
wouldnt the sabot have more surface area for friction?. As apposed to the spitzer bullet which has very little in contact with rifling. also can you even sabot inside a rifled barrel?

>>35177336
Depends what you make the sabot out of

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>>35174492
Such as?

>>35167606
Oh snap, sir isaac newton of /k/

>>35168844
but Q=0 while the bullet is in the barrel
and no force is imparted onto the bullet once it leaves, so the period where Q is nonzero is irrelevant

>>35169878
>implying friction coefficient doesn't account for contact area
That's where you're wrong. What you said is correct but its because we cannot determine the area of the true contacting surface. The coefficient is an application specific factor approximating a much more difficult (practically unsolvable today) mathematical problem of figuring out how surfaces are interacting on a molecular level.

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>>35176125
>If the barrel is a larger diameter, the force is smaller because the area is larger (P = F/A).
The formula directly contradicts your sentence:

P=F/A
<=>
F=P*A
=>
F proportional to A, meaning the force is larger because the area is larger. How do you think hydraulic presses work, dummy?

>>35174863
Dude just give up. He specifically mentioned "revs" when he listed higher ANGULAR VELOCITY as the goal of F1 engines. Your example of fluid exchange is included in his description of the quest for higher angular velocity.

To those of us with an education it is pretty obvious who went to BBC.

>And no, that's the point here, the amount of gases doesn't stay the same
jesus dude, now we know that YOU are the one with incest fantasies.

>>35175949
Finally we have a winner

>>35176256
>Playing a male (male) character.
did lol

>>35175913
Engineer here, on a surface level, this is correct assuming the propellant burns at the same rate. The only thing that makes me hesitate saying it's right all the time is the fact that the primer on the opposite end from the bullet. So the powder starts burning from the back and expels unburned powder into the barrel that burns as the bullet travels through the barrel. This means the larger diameter barrel has the potential to burn all of the powder in a shorter barrel length because the wad of unburned will potentially form a larger surface area of powder in respect to the ignition source which will speed up the burn rate. This will mean that at shorter barrel lengths, the sabot will likely be faster and in longer length barrels the properly sized projectile will likely be faster.

TL:DR this: >>35175949

>>35177882
Even if you just assume you start with equal amounts of compressed gas, the larger diameter bore will still accelerate more quickly at the start (due to its larger surface area), favoring a shorter barrel.

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>>35167583
Listen up, faggots. Integrate along barrel length, and what do we find? Bigger bore has lower velocity. Correct me if I'm wrong.

v_0=chamber volume
k=ratio of large bore area to smaller one

>>35178233
>ideal gas law
>non-ideal system
>fails to take into account non-conservative forces
Sorry pal, but you're wrong.
Easiest method would be write a simulation for it. The reason I cannot say whether or not the muzzle velocity of the larger bore would be higher or lower is because the sabot can offer a lower coefficient of kinetic friction throughout the length of the barrel. This could likely be a much more profound effect than the small change in bore diameter.

>>35177336
I know it sounds counter intuitive, but bearing surface isn't used to calculate force of friction, only coefficient of friction which is a constant determined by the materials involved and the normal force.

>>35177646
It is more aptly based on material deformation as well as surface roughness, which is more of contact surface per unit area. Overall bearing surface is not accounted for

>>35177087
People like to say engineer as a blanket term, but I hope they're civil engineers trying to flex their muscles, and not actually ballisticians

>>35178233
your integral is wrong. what you have is an expression of pressure, not force. you need an additional factor of k on the top.

aside: k is not a ratio. you're not taking a ration in this problem. k would be the cross sectional area of the barrel

>>35178299
>ideal gas law
>non-ideal system
Like everyone else is assuming?
>sabot can offer a lower coefficient of kinetic friction
Sabot also has more atmospheric drag in the bore

>>35178353
You know that pressure integrated over a volume is energy, right?
>you need an additional factor of k on the top.
Then I would be scaling the energy by k, and it would cancel out.
>k is not a ratio. you're not taking a ration in this problem. k would be the cross sectional area of the barrel
Think about it a little more.

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>>35178527
>it would cancel out.
no. it would still exist inside the logarithm
>think about it a little more
i did. you're still wrong.

>>35178574
>it would still exist inside the logarithm
Oops, you're right.

>k is not a ratio. you're not taking a ration in this problem. k would be the cross sectional area of the barrel

I still don't know what you're saying here though.

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>>35178648
I have no idea how you would think you could take a ratio within this expression. if you want to take a ratio of pressures or forces, you would end up with a unitless expression that you couldn't integrate over.
if we take the ratio of energies given different cross sections "a" and "b" we get pic related.
same with forces

>>k is not a ratio. you're not taking a ration in this problem. k would be the cross sectional area of the barrel
I had misinterpreted your work because it didn't make any sense to me. I reduced your volume integral to a 1D length integral that would yield volume. (volume of a prism is area * length)

>>35178727
Your [Vo+al] and [Vo+bl] terms are flipped in the final product of the force ratio, but the gist is the same

>>35178811
>flipped
woops, you're right.

>>35178727
I'm not integrating the ratio. If the area of the small bore is a, then the area of bigger bore is k*a, where k>1. So the volume of the bigger bore would also be k*v_{smaller}.

> I reduced your volume integral to a 1D length integral that would yield volume.
That is essentially what my integral does.

>>35178527
>atmospheric drag in the bore
We are not concerned about drag here, we are concerned with compressibility of the gas, which is effectively the same in both cases as the difference in bore diameters make it negligible.

>>35178847
oh that makes sense.
you still need a k on top for the same reason you presented me

>>35178023
He just said that in that post you goddamned ape.

stick a pole in both barrels, point them straight up, and see which one reaches peak height faster. Simple.

>>35178949
He didn't, he said that he thinks the powder burn rate would lead to the large bore accelerating more rapidly, while I brought up the fact that even in an ideal system with instantaneous burn the large bore would still accelerate more rapidly.

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>>35167583
7.92×94mm Patronen is a close counter part to and m904 slap 50bmg

velocity is around 4000 fps

It's not and exact comparison but they are both rather similar in performance .

Now which is better ?

Well 50BMG because of the versatility of having a larger bore , so more projectile options

Also have the benefit of history to show the design failure of the Patronen

this thread is top autism

I fucking love it

>>35178861
??
I'm no aerodynamicist, but the air that is compressed in front of the projectile is form drag, is it not?