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Military Guns and Ammunition

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This is intended for people interested in the subject of military guns and their ammunition, with emphasis on automatic weapons.

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PDW again   Small Arms <20mm

Started 20-Dec by DavidPawley; 31524 views.
JesseH1234

From: JesseH1234

4-Feb

stancrist said:

It does not seem sensible to me to set a purely arbitrary figure for muzzle energy. What I think would be sensible is to decide what performance is wanted, then design the gun and ammo to achieve that performance.

Plus 1-1.5kj is just about the range of 5.45 and 5.56, the lower end out of particularly short barrels.  Also any ultra 9mm or uber-toke is still going to have cartridges similar in weight and bulk to 5.45 and 5.56.

Normally I don't like high pressure cartridges for military applications, due to the barrel heating and weapon battering; I suspect there is a reason wartime German and modern Russian and Chinese cartridges operate in the low 40k psi range generally. 

However, for the stated purpose of a PDW, I think the 5.7 kind of nailed things; you get a meaningful reduction in cartridge weight, increase in capacity, and capable of being fired out of a very light weapon.  And the high pressure will not matter much, because these things by definition aren't being actually shot all that much.  It's flat shooting, stays supersonic for 300-400m (I think).  While it's no elephant gun, anything short of 30-06 will have some "stopping power" complaints.

I liked Tony's idea a while back, which assuming I am recalling correctly (although maybe I am embellishing a bit) was basically a FiveSeven with a detachable stock of some kind.  Add a 7-8" barrel (to get most of the cartridge potential), a small flash hider, and a small red dot in a holster that fits it, and I bet you could get a nifty little package.  Which, along with a decent amount of ammo, say 100-120 rds, would still probably weigh 2kg or less total. 

Otherwise, 5.45 is pretty efficient out of a 12-13" barrel, and ak stocks can fold.....

stancrist

From: stancrist

4-Feb

graylion said:

So what do we want. Penetrate a IIIa helmet at what - 200m? 150?

Well, if we're talking about a PDW to equip non-infantry in a 6.8 NGSW future, and since NGSW is meant to defeat Level IV body armor, shouldn't the PDW also be able to punch through Level IV armor?  Not out to the extended (600 meters) range of NGSW, of course, but at the shorter engagement distances likely to be encountered by rear echelon troops, say 100 meters or so.

stancrist

From: stancrist

4-Feb

JesseH1234 said:

...for the stated purpose of a PDW, I think the 5.7 kind of nailed things...

5.7 does have some desirable aspects, but it was created before the proliferation of Level IV body armor became an issue.

graylion

From: graylion

4-Feb

well, 5.45x39 has 1.75cc capacity and ~1300J ... 1400J. I get 1500J to 1600J out of a 22mm long cartridge with 1.22cc and much higher pressure in a 10" barrel. We should also remember that both materials and heat treatment have massively progressed since WWII and even the early 70s when 5.45x39 was developed. And a PDW is no meant for regular engagements. It is an "oh f*ck" weapon.

So, we can have similar performance to 5.45x39 in a much smaller frame, especially if we use a larger calibre like 6.5mm.

graylion

From: graylion

4-Feb

stancrist said:

5.7 does have some desirable aspects, but it was created before the proliferation of Level IV body armor became an issue.

Well, nothing short of a .50 BMG seems to penetrate Level IV, so we can discount that I think. 

nincomp

From: nincomp

4-Feb

stancrist said...

5.7 does have some desirable aspects, but it was created before the proliferation of Level IV body armor became an issue.

When the 5.7 is mentioned, I picture its use as depicted in the Star Gate television series where something like a P90 is used as a bullet hose that eventually hits an area with low enough protection that it can do some damage.

 

edited to make sense (ie replaced "penetration" with "protection")

  • Edited 04 February 2021 19:48  by  nincomp
JesseH1234

From: JesseH1234

4-Feb

I mean I agree about the "oh eff" part.   And I get that you can do cool things  by playing with larger bore size make more efficient use of that pressure.  However.....

I looked around to find what your proposed round was, and respectfully I would suggest that not only is a cranked up .357 sig going to weigh more than 5.45/5.56, either the bullet is going to be really light for caliber, and have low sd/bc, or it will be heavy AF.  Also the recoil might be far higher.  My quick back of napkin math was 74% higher bolt thrust vs. 5.56 (for a .357 sig case at 77,000psi), but don't hold me to it. It's also going to have longer/ bulkier mags because of the wider base.  So the weapon likely won't weigh less than the lighter .22 caliber rifles around, or it would be a beast.

Don't get me wrong I''m not making fun of you, I've had similar though experiments as this thread (ultra 9, uber tok, the new BRNO cartridge), I'm just voicing where I landed: those darn Belgians may have got this one just about right.  On the other hand if you could design a cheaper gun for the BRNO or your cartridge, I'm sure American civilians would buy them like crazy. 

stancrist

From: stancrist

4-Feb

graylion said:

stancrist said: 5.7 does have some desirable aspects, but it was created before the proliferation of Level IV body armor became an issue.

Well, nothing short of a .50 BMG seems to penetrate Level IV, so we can discount that I think.

Hmm.  Has testing shown the 6.8 NGSW candidates are incapable of penetrating Level IV armor?

stancrist

From: stancrist

4-Feb

nincomp said:

When the 5.7 is mentioned, I picture its use as depicted in the Star Gate television series where something like a P90 is used as a bullet hose that eventually hits an area with low enough protection that it can do some damage.

Yeah, that method has been advocated by some here.  I'm skeptical that the military would even consider adopting it.

nincomp

From: nincomp

4-Feb

Well, in the TV show it took about 50 rounds per alien, so, using logic, physics and all that good stuff, we could scientifically estimate 25 or so rounds per human bad guy.  That is a lot, I guess.

  • Edited 05 February 2021 0:39  by  nincomp
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