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armour piercing ammunition   Ammunition <20mm

Started 28-Dec by graylion; 3015 views.
gatnerd

From: gatnerd

29-Dec

"What works better (ceteres paribus), a lighter and hence faster bullet or a slower and heavier bullet with a higher sectional density"

The problem is different armors have different mechanisms of penetration.

Kevlar soft armor is defeated in multiple ways: High velocity (impact velocity over 2000fps) narrow cross section / pointiness (.224 55gr spitzer FMJ will pierce IIIA at 1000fps) or high hardness (steel core 9mm will penetrate 2x IIIA vests stacked on top of one another.)  M855A1 is reportedly capable of piercing IIIA beyond 1000m, due to being both pointy and hardened steel. 

AR500 steel is destroyed by velocity; a 5.56 55gr M193 at 3180fps+ will burn through a 'Level III' AR500 steel plate via adibiatic sheer. This same plate will stop steel tip M855 at a slightly lower velocity. 

On the flipside, Level III UHMWPE will catch 3300fps+ lead core M193 and .308 at 2800fps, yet can be penetrated by a steel tip 5.7x28 at 2100fps. Here, projectile hardness and pointiness is what defeats the armor. 

And ceramic defeats both high velocity and steel tips; here its really a matter of Tungsten cores of sufficient length and speed to penetrate. 

Making this even worse, most 'Level III+/Level IV' hard armor is a mixture of Ceramic and UHMWPE. So one must design to punch through two different materials back to back. 

  • Edited 29 December 2020 4:09  by  gatnerd
graylion

From: graylion

29-Dec

so I am fundamentally thinking a hardened steel core like the 855A1 in a 1300J PDW round (modernised version of 5.56x30 MARS).

RovingPedant

From: RovingPedant

29-Dec

But what targets are you intending to defeat?

 

graylion

From: graylion

29-Dec

PDW role - so near peer combatants.

RovingPedant

From: RovingPedant

29-Dec

So soft armour with rifle-proof plates, probably ceramic.

I doubt you’d make it through the plates with a PDW, so you’re left going for soft or no armour. I suspect that narrow, sharp and fast would be the order of the day.

Fast also compensates for aiming errors by inexperienced users.

The real trick is to transform the high velocity into terminal ballistics, either post armour or hitting unarmoured parts

smg762

From: smg762

29-Dec

With energies of roughly 1000ft lbs,  a 19.  Caliber would have by far the best energy retention at 300m.  A 6mm wouldn't come close.  

If penetration must be extreme,  you'd want a fairly 'full' shaped bullet,  closer to 556 shape than modern,  pointy,  VLD shapes.  This would allow an extremely large steel core,  which is far more economical than tungsten. 

Finally though,  slimmer calibers do struggle in short barrels,  energy wise.  Because the swept volume is less. 

A mars-style round would need at least 19 inches of barrel to reach 1300jouls,  if the caliber was. 19 (5mm)

Your PDW should therefore be a bullpup,  which uses reverse feeding (like the boberg pistol) to shortern the overall length.   Lastly,  you'd want the magazine right at the very rear of the bullpup.... far away from the grip (again this shortens length).... also,  don't use a flash hider.  That would add an inch of length. 

Ultimately you can get extreme 300m penetration with far less energy.  An. 18 caliber,  with about 750 ft lbs and a steel core,  would do the same job.  From a 15inch barrel. 

graylion

From: graylion

29-Dec

I am going for something that can be carried in a thigh holster - like the Keltec gun we are discussing in the other thread. 

Where I am at is this bullet: http://www.geoffrey-kolbe.com/cgi-bin/drag_working.cgi?unit_length=mm.&weight_unit=grains&bullet_name=GLS+PDW+II&re_calculate=yes&boundary_layer=L%2FT&diameter=6&length=28&nose=14&meplat=0&drive_band=6.15&base_diameter=&angle=7.1&boat_tail=5&secant_radius=6.6&weight=62.3&density=8.12

which with my cartridge gives me 1417 J aka 1198 ftlb at a V0 of 2755 ft/s. At 300 yds it retains 2031 ft/s at an energy of 651 ftlb. This is from a 10.5" barrel, using drive bands. 

What concerns me is the muzzle pressure of 13.500 psi.

  • Edited 29 December 2020 8:34  by  graylion
smg762

From: smg762

29-Dec

The keltec gun could never work in thigh holsters.  The magazine is extremely wide... and that means the gun is too. 

If it must be holsterable,  you want a gun with the magazine in the grip.... like an MP7. 

to get acceptable energies you'd need a cartridge that resembles a fat 10mm/. 45,  necked down to small caliber.  The grip needs careful design to remain comfortable.  You could just about get a mars-sized round but it would be shorter and fatter than the mars. 

1100ft lbs from a 10 inch barrel is completely impossible with a mars sized round. Swept volume plays a massive role.  You'd need a 7. 62 bullet to get that kind of short barrel performance. 

The mars had 830 ft lbs from a 10 inch barrel - and it still had pressure problems. 

Also,  6mm @ 1100 ft lbs would not be  Pleasant or controllable in a light holsterable thigh gun.  even from a 3kg M4 carbine the felt recoil would exceed 556.  

My suggestion (for a holster carbine)

MP7 style weapon with 11. 5 inch barrel.  Uses boberg-style reverse feeding.  And the grip/mag is set very far back,  just like the prototype MP7 (Google it). 

Stock is side folding to reduce length. Total length matches the MP7 

Caliber is basically a 10mm or. 45 sized round,  necked down to. 20 caliber.  Far more controllable. Energies of 850ft lbs are recommended,  with heavy 47 grain bullets. 

  • Edited 29 December 2020 9:20  by  smg762
gatnerd

From: gatnerd

29-Dec

graylion said:

so I am fundamentally thinking a hardened steel core like the 855A1 in a 1300J PDW round (modernised version of 5.56x30 MARS)

Chinese Level IV bought for less then $100 per plate on Aliexpres is stopping M2AP fired at 3000fps+ from a .300 Win Mag from 45' away. Its stopping 7.62 M993 Tungsten at 2750fps impact velocity. Its stopping .338 Lapua Tungsten from 200yds...

The point being that any rifle round, much less PDW round, is no longer really armor piercing against hard torso armor. AP is only relevant for a PDW in terms of penetrating the IIIA helmet. 

I suggest checking out Buffman's youtube channel for a look into what modern armor can handle.

dobrodan

From: dobrodan

29-Dec

If I had been a REMF, I would have loved something like the KelTec SU-16 C with a 12 inch barrel, with a small suppressor, and carried it in a holster, stock folded, with a 20 round magazine.

It is light, compact, cheap, and easy to maintain, while using the same ammunition and magazines as the M-4/M-16.

 

  • Edited 29 December 2020 13:38  by  dobrodan
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