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patent for an MP7 in 300blackout   General Military Discussion

Started 17-Oct by smg762; 4470 views.
nincomp

From: nincomp

1-Nov

smg762 said:

Frankly the best compromise is a 7.5FK with very lengthened bullets....taking the OAL to 44mm

This sounds much like a shortened .30 HRT.   Pretty easy to do since it starts with 6.8 SPC/ .224 Valkyrie brass.  I am not sure that sticking with a roughly .30 cal projectile is the best choice, though.

 If you have not read it already, Tony has a good article on PDW's that shows a lot of cartridges side by side (https://www.quarryhs.co.uk/PDWs.htm).  Nathaniel also did a number of good articles like this one when he worked for TFB (https://www.thefirearmblog.com/blog/2017/02/20/modern-personal-defense-weapon-calibers-004-7-5x27mm-fk-brno/).  Use TFB's search function for others.

SMG762, at the risk of being pedantic, I think that I understand Roguetechie's frustration and will try to explain.  Please forgive me if you already know all this.  You are at a bit if disadvantage on this site since the PDW concept was extensively discussed on this forum a number of years ago.  Many here have either already come to their own conclusions or have given up on the matter.*    In short, a PDW using something like .300 Blackout or 7.5 FK made a lot more sense before body armor was commonly encountered.

The concept of a PDW is broad, so it is important to determine what exactly the weapon is intended to do, at what range, and how it is going to be carried.  If the goal is 100m or less against unarmored opponents, you can end up with a pistol that has a folding or retracting stock like the Crist PDW.   These are small enough to be worn while on duty.   To meet the portability requirement, almost all of this style of PDW have magazines inside the grip.  The main problem with the pistol-based PDW's is that they work best against opponents without body armor.   It can be argued that equipping soldiers with weapons tailored to the local threat would be useful, but that is not how the US and many other countries do things.  They prefer to reduce the inventory of weapons rather than utilize a "golf-bag approach" where the soldier could choose from numerous alternatives.  Instead, they have decided to arm against peers and near-peers who are likely to use body armor... or ignore the issue and just stick with a pistol.

Everything changes once you face an opponent wearing body armor.  Here, even dedicated AP ammo in a pistol-based PDW has a very limited effective range, if indeed, it is effective at all.   The 6.5 CBJ is indeed designed to defeat some body armor, but many people have significant doubts about the terminal effect of the small diameter penetrator.  In the end, the best hope of someone using a pistol or pistol-based PDW against an opponent wearing body armor (other than run-like-hell) is to keep firing and hope to hit some spot that is not well protected.

If you want more rifle-like performance, things get ugly fast.  Much beyond 100m, the aerodynamic efficiency of the projectile becomes more important and the length-to-diameter ratios of the bullets begin to grow.  The weapons themselves get big enough that they begin to get awkward to carry full time (the Crye hopes to be an exception to this).  Another thing that changes with "rifle-like" performance is the wounding mechanism.  Although this is less well defined, in general, with a rifle-like wound, the combination of high velocity and sufficient effective frontal area** of the projectile cause tissue stretching and tearing around the wound track.  A fragmenting bullet can cause even more damage, with the fragments cutting stretched tissue. Sometimes the rapid displacement of tissue from the temporary cavity is enough to cause a stunning effect that temporarily disables the victim.***  Although the velocity to achieve this effect varies with the effective frontal area and the location of the impact, the information that I have seen indicates that it seldom occurs with a projectile velocity much below 2000fps (600mps).   Alternatively, the damage from a "pistol-like" wound is from the hole the bullet punches during its travels.  Neighboring tissue and blood vessels are left intact.  Big hole wounding, in other words.

Once body armor penetration enters the equation, the retained "specific energy" (energy divided by frontal area) of the projectile becomes more important than total kinetic energy.    The force must be concentrated into a small area to defeat the armor before it can reach the wearer.  It is the difference between shot with an arrow and being hit by a baseball, even if both arrive with equal energy.  One penetrates the other doesn't.  This is why the reasonably high muzzle energy of the 7.5FK or .300 Blackout won't necessarily translate into good body armor penetration.  The .221 Fireball may be more effective, even though it has significantly less kinetic energy when shot from a very short barrel.  

After a projectile has succeeded in penetrated the armor, what then?  It is unlikely to retain enough velocity and energy to act "rifle-like."  It might take a lot of holes to stop the opponent.  I always come back to picturing scenes in the sci fi television show "StarGate", in which bad aliens were liberally hosed with dozens of rounds from P90's.  Wasteful, maybe, but it at least saved the Earth.

For a short-barreled weapon,  I would like to see more development put into sabotted loadings, or maybe even more exotic concepts like squeeze bore.  The idea is to maximize the base area while in the barrel to extract as much energy as possible from the propellant, then send a smaller diameter bullet downrange.  Although sabots have been around a long time, I have not seen much about accuracy.  There is little point in sending a bullet downrange if it won't hit its target. 

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  • Edited 01 November 2021 19:54  by  nincomp
smg762

From: smg762

1-Nov

Im well aquainted with penetration and i know a 300 weapon would have awful penetration compared to a CBJ or hot- rod 4.6mm

I read the PDW thread years go. My own design uses a large cartridge like the 224 boz or better, the 224 JAWS

This would be necked down to about 4.9mm, with a hefty 600ft lbs in 6 inch barrels - far better than HKs 4.6

smg762

From: smg762

1-Nov

Rogue, do you think the crye gun could be made more compact by shortening the rear reciever to almost nothing?

Instead a small slide would pop out the rear of the gun with each shot

Would this system be strong enough for rifle rounds?

roguetechie

From: roguetechie

2-Nov

Yes, you probably could do that. I don't necessarily know how safe it would be though. That's essentially what the original amt automag did as well as the mars pistol which was a beast of a pistol from the dawn of the automatic pistol era.

It's not a solution I'd be tempted to go for but there's no specific reason you couldn't do it

smg762

From: smg762

2-Nov

I was thinking in terms of a handgun that can share ammo with the rifle.

Lighten the crye gun to 1kg and usr shared mags for sidearm and long arm

roguetechie

From: roguetechie

2-Nov

That's a taller order than we can actually pull off lol!

Don't get me wrong, that would be awesome.

It's just sorta beyond our capabilities to produce.

Also, sharing magazines seems like a really cool idea on paper but it's not necessarily something worth making the compromises you'd have to make to get there.

If you go down that road you either end up with something like the gwinn arm gun/Colt imp (picture below) 

Or the Magpul PDR 

Neither of which are going to weigh 1 kg or holster particularly well.

Also 1kg empty weight even without a magazine doesn't give you much room to work. My two favorite machine pistol designs of all time (Because I think they got closest to hitting the ideal) are the Colt SCAMP and the Robinson model 11 neither of which met your weight bar. (guns.fandom has good Robinson model 11 information)

smg762

From: smg762

2-Nov

Yeh i was more curious about the feasibility from a mechanical perspective....a hypothetical automag action with crye angled ammo

It just seems you could lose strength by going from the normal 'mac 10' shape to a small movig slide

You could use the saved length to add more.barrel and avoid thr flash problems of 556

roguetechie

From: roguetechie

2-Nov

Oh you almost certainly could go to a more automag like action and that could be pretty interesting.

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