Could the 5.45x39 out do the 5.56x45 in combat weight efficiency?

>>34983639
That's too close of a difference for anyone that doesn't have profound autism to actually care about.

Not by much, the steel cases are enough to offset the weight advantage from the shorter case.
5.45 outdoes 5.56 in ballistic coefficient and has a better case taper, but at the end of the day there isn't a great difference to justify one or the other beyond politics (for militaries) or what gun you want (for private owners).
6.5-7mm class projectiles seem to be the trend for getting better performance from an intermediate round.

>>34983667
>>34983672
Yeah true.
5.56 is such a good round, it's hard to think of a replacement.
5.45 though, woah baby.

>>34983672
>the steel cases are enough to offset the weight advantage from the shorter case.
Steel is less dense than brass, though.

>>34983639
>something in the 5mmx49
You mean like 4.85x49 British? I don't really see enough difference there to really bother.

>>34983687
>hard to think of a replacement
6.5x39
Bam, done for both

>>34983639
53gr 5.45 matches 77gr 5.56 terminal ballistics and BC as well. 5.45 has a better and more reliable deformation process that causes early yaw , especially so with hybrid steel-lead core rounds like 7N6. With standard commercial lead only ammo, it matches Mk. 262 mod 0 in performance. It's almost 33% less weight for the bullet at least. Against M855 (190gr) 5.45 7N6 (162gr) weighs nearly 30 grains less per cartridge which is 85% of the weight of a somewhat comparable 5.56 round and probably even less against heavier rounds like Mk. 262.

>I was think maybe something in the 5mmx49 might be a better option for engagements close and far distances.
I'm of the opinion that we need to have a high BC 4.5mm or so round that has either similar velocities to 5.45 or slightly less and focus on making the rounds even lighter with lighter recoil. For all the wonders that 7.62 NATO has 6.5 Creedmore does everything better. We need to make a smart cartridge design with 5.56 like how 6.5 CM is against 7.62 nato. I imagine with a good BC 4.5mm round we can get similar wounding potential to mk262 while having extremely lightweight rounds with minimal recoil that would allow troops to carry more and be much more efficient in burst/full auto for increased hit probability and a more efficient combat load overall.

>>34983869
>6.5x39
Probably not the best choice when you factor in a lead-free projectile going forward.

>>34985834
>I'm of the opinion that we need to have a high BC 4.5mm or so round that has either similar velocities to 5.45 or slightly less
Yeah, I don't know about that.

>>34985834
Just as >>34983667 said, too close of a difference for anyone that doesn't have profound autism to actually care about.

>>34986385
That's nothing any intelligent country is doing, though

>>34986419
Why not? A hollow tip, high BC, is the similarity between commercial ammo 5.45 and mk262 in terms of all their characteristics. A smaller round with even higher BC and similar terminal instability like with 5.45 would seem to be a real breadwinner in terms of reducing weight, recoil, as well as keeping terminal ballistics.

>>34986425
That's why I suggested designing a round that is more like 5.45 but in an even smaller caliber that gives more of the intermediate cartridge advantages of lighter weight and less recoil while making the standard loading a high BC so it can still work for longer ranges than PDW rounds. Maybe 4.5x35 or so. Instead of a 15% reduction in weight for similar capabilties, why not reduce the weight dramatically by something like 50% or so?

>>34986429
Lead free is how you get long, low-drag, but leaning towards light-for-caliber so you can still get a more premium velocity. Long, low-drag lead bullets in 6.5 Grendel are pretty slow, even with full length barrels.

>>34986509
>Why not?
They came up with something similar with the 4.5 Interdynamics and it didn't really go anywhere. If you were going to drop the caliber down even further, I say make the case bigger and crank the velocity up like .204 Ruger or .22-250.

>>34983639
No because the weight is so marginal in difference that it would not matter.

>>34983672
>better case taper
There's no need for more taper on the case than there is with 5.56 NATO.

>>34986532
>Lead free is how you get long, low-drag

Wrong. Lead free is essentially supercharged hunting rounds to satisfy the humanes of a quick and reliable death to the animal. That is why .243 is the minimum for hunting but varment soft points are about the same as 5.56.

>>34986627
>implying 5.56 doesn't suffer from more stuck cases and case-head separation than 5.45

>>34986598
It's a matter more of the procurement process being lousy than Kelgren coming up with a bad idea. His gun was a little wonky, though but the cartridge was a good idea. You don't really gain anything useful from a hyper-velocity round from a soldier's perspective other than more recoil. The increase in range isn't worthwhile since most soldiers have a tough time shooting past 200 yards under mild stress anyways. You might as well min-max letting your infantry handle close and medium range while letting crew served guns and DMR/Snipers to get the long range stuff.

>>34983639
Fun fact: many benchrest wildcats ultimately derive from the x39 case

>>34986641
>long, low-drag, but leaning towards light-for-caliber
A lead free bullet of the same size and shape as a lead bullet will be lighter. In a military context it has nothing much to do with hunting bullets, which are typically solid copper or brass with a hollow point. I'm talking more along the lines of the EPR ammunition.

File: 5.56x45 vs 5.56x38 - Copy.png (65KB, 191x320px) Image search: [Google]

65KB, 191x320px

OP, related concept: 5.56x38 FABRL
-high BC bullet
-lower weight bullet
-same velocity/trajectory as 5.56
-smaller case
-less powder
-lower pressure
-lower recoil

>>34983850

4.85x49 is not 5mm retardo maerquiz.

>>34986627
it could allow steel case ammo though. Lighter and cheaper.

>>34988556
http://www.thefirearmblog.com/blog/2016/08/12/modern-historical-intermediate-calibers-011-5-56x38-fabrl/


Damn, what a banger. It doesn't have the power but fuck me it can fly.

>>34988564
>4.85x49 is not 5mm retardo maerquiz.
It's 5mm on the nose.

>>34988577
>it could allow steel case ammo though. Lighter and cheaper.
NATO countries are more likely to switch to polymer cased ammo.