What would you say is the optimal number of rifling lands /k/?

>>34144742
I heard someone say 1/8 or 1/7 for 5.56 I'm not sure if that means anything though I'm a noguns. Apparently it's the most common but I'd google it as a starting point.

>>34144742
Also how does barrel length factor into this?

Theoretically it seems to me that this is a factor of caliber v. length, given that contact with the lands will soak kinetic energy as it clears the barrel.

For reference the first mockup I made there with the 12 lands (at 0.1mm height btw), is a 550mm barrel. So again, looking around it really seems like overkill.

Do you reckon this would lead to a gun jam or at least significantly lessen bullet velocity?

>>34144765
That's twist rate, not haw many grooves there are

>>34144742
The British did some tests and apparently two grooves is fine to stabilize a bullet. Of course with modern button rifling there's really no downside to having more.

>>34144742
As i understand it, more ridges (assuming that's what you mean by lands) means more contact, but it'll also be less sturdy.

Things like 20mm have only a few because it would wear out too easily otherwise (i think 4 if i remember correctly). I know because my dad has a pair of vulcan barrels that were thrown away

Artillery i think has two if it's rifled at all.

In contrast, what if you upped that number to, say, 100? You can see how fragile it would be

>>34144801
Isn't there? Cause I'm mostly concerned about this

>>34144770
>Do you reckon this would lead to a gun jam or at least significantly lessen bullet velocity?
>>34144819
>In contrast, what if you upped that number to, say, 100? You can see how fragile it would be
Can you explain how that happens? Cause coming at it theoretically, it seems like the added thickness would just enhance the metal's structure, though I could see wear being more likely to jam it.

Just to be clear guys, I'm coming into this as a greenhorn to gun design and trying to make this as optimal as I can out of the gate. That said the first concern that occurs to me is impact on muzzle energy. How would you say more ridges and a longer barrel factor into that?

>>34144850
I'm using a 12 inch revolution pitch for the .45 barrel btw. How do you think I should scale that as the caliber increases/decreases?

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>>34144742
look at any modern pistol
there are very few helical crenalations and merlons in the barrel
and they are very shallow indeed
nothing deep like that tank barrel pictured
the more lands you make, the more surface area, and therefore more friction you have with the bullet
increases the chance the bullet gets stuck
...
machining practices and economies of scale dictate a consistent helix
you could experiment
a helix that twists more aggressively as it goes to the muzzle
perhaps start the helix at 1:8 for first 1/3 barrel, 1:7 for middle of barrel, then 1:6 for last 1/3 of barrel
run this hybrid twist against factory barrels and see if the rate of acceleration of the twist is better
wish i was a machinist some days

>>34144742
I believe Marlin works with the "many many lands" theory of rifling, they call their system the Micro-Groove barrel. They swear up and down it gives better velocity.

Charter Arms does something similar, they increased the number of lands from four to eight, I think. Similarly, they say they get better velocities from their li'l snubs, than compared to the competition.

I'm guessing, but I think with more grooves, the grooves don't have to be as deep, so perhaps the inner diameter of the barrel is effectively larger and therefore not as tight a squeeze for the bullet, thus impinging less on it's velocity? While still having the same stability effect?

>>34144770
I read an old article about a custom .45-70 that claimed they got better velocity from a cut down, shorter barrel than the traditional length. I forget the exact lengths, I think they cut it from 18" or 20" to 16". They were a little surprised, but theorized it was a matter of bore friction.

Might be something to that, aren't most .45-70s pretty short these days?

Shit, tovarisch, I'm not an engineer or machinist. You're way beyond me. Please keep working on it and post results.

>>34144742
Zero. Be a man.

>>34144992
optimal kek achieved

>>34144983
>Please keep working on it and post results.
Will do.

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I'd say that the optimal number varies a lot because there are some issues to consider, first I'd say that caliber dictates a lot because not only a bullett need to be stabilized good, but also a rifling must not steal muzzle speed yet has to be durable.

For example, I'd always like to see some few but fat and deep lands in a magnum gun, and I'm fine with my Marlin 60 with those ghostly microgrooves as they will only meet soft lead in their use.

Also, if a barrel is made with a proper process like hammer forging achieving a good hardness, that will only help with lifespan of the rifling.

tl;dr if metal quality is fine 4-6 lands are enough


>>34144992
pic related

>>34144912
>and they are very shallow indeed
>nothing deep like that tank barrel pictured
Anon the grooves in that tank barrel are pretty shallow — relative to the projectile diameter, which is what I think would be the important bit.

>>34145035
Just a random thought, do you suppose you could offset any friction by ramping up bullet velocity per caliber if you replaced the firing pin with a plasma mechanism?

What I mean is, rather than relying on a pin strike to ignite the cordite, flooding the chamber with compressed argon, hitting it with a microwave burst to create a plasma and then letting the heat from it ignite the cordite?

I reckon the barrel needs to account for increased tensile stress but when the gas expands as it ignites, it doesn't flood the chamber and then push back against the bullet, but rather hits a wall of intensely pressurized gas right away. If the argon doesn't contribute to velocity then at least it should redirect a lot more force into the bullet no?

>>34144983
>They swear
>they say

100% marketing wank.

>>34144912
Progressive rifling has never been show to improve anything.

>>34144859
As per the Miller equation, at least across the caliber ranges for small arms.

>>34144801
My rifle barrels with the best blend of velocity and accuracy are Pac-not 3 grooves. Never owned a 2. Unfortunately Pac-nor isn't what they used to be, and no one makes are good 3 groove these days.

>>34144770
Barrel length doesn't figure into it. Lands don't 'soak' energy any more than grooves do over the length of the barrel, beyond the some additional drag from the very small surface area increase additional l/gs add.

>>34144742
There isn't an optimal and there are many more important factors in a barrel's construction.

>>34144765
The twist rate for long barrels is very specific to the type of ammo used. There are a few types of 5.56mm that were designed for certain types of barrels.

>>34145083
>Lands don't 'soak' energy any more than grooves do over the length of the barrel, beyond the some additional drag from the very small surface area increase additional l/gs add.
Really? It's that negligible?

>>34145061
>grooves in that tank barrel are pretty shallow
false
you don't have my engineering degree
nor do you have my DoD experience
but you do have an audience of anons equally as ignorant as yourself

>>34145081
Your arrange would drastically increase lock time, and the transit time for the bullet through the barrel, which would likely degrade accuracy beyond any advantage to same conferred from the additional velocity.

Not that there would be any additional velocity....the peculiarities of bullet obturation are not well understood but due to the way powder burns (pressure actually 'ramps up' as you describe) obturation differences don't appear to be significant factors in muzzle velocity.

>>34144742
the bullet should expand to fill the barrel, so the amount of friction should be unrelated to the amount of lands, except for a tiny additional amount due to the sidewalls of the lands. you will lose energy due to deformation of the bullet to fit the lands, so fewer is probably better. i would suggest minimum 3 as small as possible to ensure good rotation. consider that the amount of material displaced by the land has to be enough to form a seal between bullet and barrel, if the bullet has poor qc and is slightly undersized

>>34145083
>Progressive rifling has never been show to improve anything.
false
the helix is complicated but so long as the helix progresses as the bullet accelerates, it does show small improvement

>>34145083
>Barrel length doesn't figure into it. Lands don't 'soak' energy any more than grooves do over the length of the barrel, beyond the some additional drag from the very small surface area increase additional l/gs add.
Transferring directional velocity into rotational velocity does calculate into it.
The area between the lands and grooves does.
Love that crenal and merlon terminology...

>>34144801
Did some tests, hell they made a shitload of Enfield No4's with 2 groove's and mine shoots pretty fucking good.

Alot of bench rest shooters go for 3, 4 or 5 groove rifles.

>>34145120
No, it hasn't.

It certainly does not figure prominently into any current small arm accuracy discipline's top rankings.

>>34145232
>No, it hasn't.
CNC controlled EDM grooves, variable helix
It fucking works, dawg
>It certainly does not figure prominently into any current small arm accuracy discipline's top rankings.
Da fuq did this moron say about competition rankings?

>>34145147
The number of l/gs doesn't affect the amount or rate of conversion of energy from the propellant

And yes thank you for repeating my assertion that the increase in bearing surface of the barrel resulting from an increase in grooves (given the same depth) will affect velocity. It is a rather small impact, given the many other factors in determining that output.

>>34145269
I'm well aware of the many techniques for rifling barrels.

Please link to competitions where progressively rifled barrels are dominating.

>>34145293
>Please link to competitions where progressively rifled barrels are dominating.
I never said they were used in competition
That's what I inferred from your reference
I play around with scrap at work with CNC, EDM machines.
Haven't made anything for myself.
And the materials are shit for funs anyway.
>boss: hey, whatcha doin with that cold hammer forged shaft
>me: erm, nothing, sorry, getting back to work
so when I have a piece of shit bar stock and play around it doesn't get noticed,
especially since the other shit machinists have a fucking scrap rate of over 10%, killing our chances at a fucking group bonus each month
I digress. It's doable, fairly easily too

In the end OP, all this is so theoretical and miniscule that the only way your going to achieve the result you want is through lots and lots of empirical testing. You cannot get this right on the first design.

I would look into doing rudimentary FEA analysis on different designs (polygon, conventional, high groove count, low groove count, etc) with Solidworks or ANSYS first before going out and ever actually making anything. Electricity and computer time costs alot less than machining 40 different barrels (which you might end up doing anyway depending on your level of precision required).

I think the first thing you should do is figure out EXACTLY what is going to be going through the barrel. Diameter, muzzle energy, barrel length and metallurgical compositions are the real things that determine what type of rifling youre going to use.

>>34147563
> FEA analysis
I'm setting this up now, though I'm using Inventor with Nastran and CFD.

>EXACTLY what is going to be going through the barrel. Diameter, muzzle energy, barrel length
This is going to vary, so I'm trying to establish some ranges for different use cases.

>metallurgical compositions
Digitally I'll test some other compositions, but really ideally I want to see if i can do this with 6061-T6 steel. Mostly because I can actually get that in filament to print, so I don't have to machine it. Should produce a solid piece within .001in granularity.

>>34144801
as you approach an infinite number of grooves, though, they approach zero width, so the limit of the function is a smoothbore. so at some point, there must be a downside to having more.

>>34148236
now this is a nigga that knows his calculus.

>>34145109
>ignored the important part
nice engineering degree, lot of good it's doing you

Twisties are Twisties - Barrel Maker

>>34144819
>Artillery i think has two if it's rifled at all.

An M777 howitzer barrel has 48 rifling lands.

>>34150899
I'm guessing this correlates to the round mass and muzzle velocity?

>>34148004
3d printing will give you really weak metal. considering barrels are hammer forged and your using sintered i think youll have some issues. you could try carburizing the inside of the barrel. also depends on what bullets youll lose, since soft lead will damage the barrel the least. also consider how the ribbed quality of the surface will affect ballistics and friction

>>34144742
5R at a minimum of 2" in length and an appropriate twist for the bullet you're designing for

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>>34144742
>What would you say is the optimal number of rifling lands /k/?
The USA is the best land for rifling. SHALL NOT BE INFRINGED.

>>34151225
>ribbed quality
This is why I'm looking into finishes, and thanks for the tip I'll evaluate the carburization. With the resolution I'm not *that* concerned, but it will probably crop up especially with curved faces yeah.

>>34144765
It must be summer

>>34144742
at least three.

>>34151416
your surface will essentially be metal P600 grit sand paper

>>34148236
but anon, 6061 is aluminum, and it's not gonna be T6 anymore after you melt it into a part, it's gonna be O which is not going to withstand substantial pressure. Of course it wouldn't really be all that hard to use a small oven to re-solutionize, quench and age it back yourself, but you might get dicked by residual stress from heat treatment fucking with your dimensions.

>>34144742
Three for three point contact.

Less friction for heat.

No lands opposite each other to also reduce friction.

>>34144742
the only downside to more lands I could perceive would be more friction=more heat.

>>34144765
Anon, he's talking about the quantity of grooves that compromise the rifling. The numbers you're regurgitating are the total length, in inches, it takes complete one full 360 degree rotation of the rifling, written as 1 (twist) : 8 (inches), hope that helps.

>>34152335
>No lands opposite each other to also reduce friction.
Thanks for that detail anon. I caught it somewhere reading about bullet pinch, seeing you confirm it I'll make sure to account for it.

>>34152314
>6061 is aluminum
It is. Sorry, I got my alloys mixed up. I got 17-4 and 316L steel though, as well as A-2 and D-2 tool steel. I figure the latter will probably be best but I can't in good conscience rule on that without digging into *that* first.

>>34152212
I realized I would have to process it. Honestly I should probably go over that with a metallurgist for the details, as well as a review of available alloys. I'm out of my depth there.

>>34152439
I believe 17-4 is a precipitation hardened steel, 316 is an austenitic stainless so if I recall it's pretty soft as far as steels go. A2 and D2 im not sure of, but they're probably ferritic or martensitic. Any of them probably achieve peak hardness via heat treatment, so if you're looking to 3d print and finish a test barrel, I think your best bet is going to be finding a martensitic steel with properties similar to whatever the best barrel guys out there are using and then doing a low (ish) temp stress relief/temper after you do the 3d print.
I'm also assuming the 3d printing is like laser or EB sintering with wire or powder, that's the only tech im super familiar with and the cooling rates on either of those are pretty damn fast, especially if you do the test under vacuum.
All that said, and I'm sure you'll be cautious, work up loads slow if you go that route and stay the fuck away from the thing while you're test firing.

>>34152439
problem is any form of treatment will deform it, which i guess is why theyre cold forged. you could 3d print the barrel with plastic, take a plaster cast, then melt out the plastic and use the plaster to make a steel mold. i think nitrogenation or carbuerization will be the lest deforming treatment you can use

>>34145109
You sound like Dwight from the office

didnt read thread ill just spout nonsense, plz correct me or expound

rifling should engage projectile long enough to stabilize/initiate bullet spin. do it too fast for too long, (1/5" in a 20" 5.56) lands tear up the jacket
do it too slow and bullet doesn't stabilize and no spinning means no accuracy, you get tumbling keyholes (1/14" in a 12" barrel 5.56)
higher bullet weights need slower twist rates for rifling to engage and have an effect (you cant do 30mph in a parking garage spiral ramp in an f-350, but a dirtbike might)
progressive gain twist rifling starts slow at the breech, ends up fast at the muzzle, and is more forgiving towards everything (its probably the best kind of twist rate, no downside other than manufacturing complexity[cost])

polyagonal polygonal rifling is pretty fucking neat, though people argue that its manufacturing process makes it inherently weaker than traditional cut-rifled barrels in regards to rifles.
my belief is that its method of proj. engagement is too different that it shouldnt be equated to traditional rifling until someone posts the math on twist rate engagement between the two across a wide spectrum of twist rates. for example, a polygonal 1/8 barrel has a different effect on the same bullet than a traditional cut rifled 1/8 of same length.

>>34151408
There can be only one

>>34152559
You're right, but also not talking about the right subject.

>>34152488
It's sintering yes. Though I can do material tests to a reasonable depth digitally, in which case I can simulate other alloys to. Leading to..

>>34152514
Yeah I was considering just creating a plaster mold for casting. Though, if I'm going that route it may be prudent to just look into forging/boring it. Although that does make rifling more challenging. It requires entirely different tools, though it would offer greater tensile strength than cast steel, question mark?

>>34152663
Absolutely. Best method would be to force a slightly oversized die down the barrel so it deform to the shape of the rifling. This would work harden it. Ideal process would be something like casting a barrel, heat treating it by tempering then annealing, then either cutting or forcing a die down the hole to get the rifling from what I know. Carbuerizing or nitrogentation might be a really good idea though, I'm kind of excited about it because it's not a technique I've heard of being used much.

4 or 5 grooves is plenty enough.

Dont know the pros or cons of more.

>>34152742
Carburizing should be relatively easy to do with little equipment - literally finely powdered charcoal stuffed into the barrel, the entire thing buried in a reasonably airtight crucible, and left at high temperature for several hours will decently carburize the external surfaces.

When you're done knock off the lid of the crucible with a hammer and drop the charcoal mass and barrel into a tank of water.

However note that this type of case hardening usually deforms larger parts.

>>34144801
The downside to there being more lands is that there is less barrel in contact with the bullet. This is going to accelerate wear on the thin lands. Throat would probably go out faster.

>>34153014
The bullet is always in full contact with the bore.
The bullet is groove diameter so the lands engrave into it.

>>34153056
Yes, but the lands take the most wear. It takes a lot of rounds to wear lands out down the length of a barrel but the blast is what takes the throat out.