gatnerd

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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modified 5.7x28   General Military Discussion

Started 10/1/23 by smg762; 1968 views.
smg762

From: smg762

10/1/23

one of my ideas for a cartridge involves a modified 5.7mm.   The case is increased to 37mm long - so its very long and thin.

the case is modified to much higher preassures, for example 70k PSI

finally, it's necked up to a 7mm bullet which is super long (38mm).  The barrel is 23 inches, and the overall length is 64mm, so the bullet is seated VERY shallow in the case - to get more powder

what sort of energies do you think it might achieve?   i want it to reach 1800ft lbs....do you think this is likely?

In reply toRe: msg 1
EmericD

From: EmericD

10/1/23

smg762 said:

finally, it's necked up to a 7mm bullet which is super long (38mm). The barrel is 23 inches, and the overall length is 64mm, so the bullet is seated VERY shallow in the case - to get more powder

If the cartridge is 64 mm long with a 37 mm case, you have 27 mm outside the case so the "super long" 38 mm bullet is going to protrude 11 mm inside the case, which seems to be much deeper than a common cartridge neck.

The case diameter of the 5.7x28 mm is only ~8 mm, so you have basically a straight-wall 7 mm cartridge, with a very limited usable case capacity (around 11 grains).

I don't know the material you want to use for the bullet, but with a lead core and a length of 1.496" (38 mm) you're aiming at something around 165 gr...

The Powley computer think that with unobtainium powders you can reach a propulsive efficiency of 65%, which is twice as much as a typical rifle cartridge, for ~1100 ft-lbs of energy.

In reply toRe: msg 1
gatnerd

From: gatnerd

10/1/23

smg762 said:

one of my ideas for a cartridge involves a modified 5.7mm.   The case is increased to 37mm long - so its very long and thin

I had a similar idea of a lengthened 5.7 cartridge, as a maximum capacity, minimum recoil assault rifle. 

However, my idea was a 5.7 lengthened to 42mm, with a VLD lead free 0.204, projectile weight of ~50gr. 

Goal was to hopefully hit 2750fps+ from a 14.5-16" barrel. This would allow for comparable fragmentation range to current M855A1, but with an increase in magazine capacity, an increase in FA controllability, and a reduction in ammo weight. 

50gr 0.192 G7 @ 2750fps = 1700fps EPR frag range @ 445m, Supersonic to 754m

~40rd will fit in a 30rd 5.56 length magazine

Recoil comfortably below 5.56 or 5.45

Unfortunately I've yet to be able to coax my friend with Quickload to draft the cartridge and run the numbers for what it would actually be capable of.

In reply toRe: msg 1
JPeelen

From: JPeelen

10/1/23

You are simply replicating the "pencil" type of long thin cases from the late 19th century, which became notorious for being ballistically inefficient. I other words, low muzzle energy per gram of propellant due to geometry against the laws of thermodynamics.   

If you only studied more closely the history of small arms and small arms ammunition, you could avoid proposing scheme after scheme that has been tried decades (if not a century) ago and turned out to have drawbacks that make it impractical.

  • Edited 10 January 2023 16:21  by  JPeelen
In reply toRe: msg 1
roguetechie

From: roguetechie

10/1/23

You're basically trying to reinvent the knoxx HEC which was a military development project to essentially make a straight wall very high pressure 5.56 that got equivalent or better performance to existing 5.56.

Knoxx was fairly close to succeeding, except for the occasional round that would have a wild "pressure excursion event" (300k psi plus near as they could tell) and blow up their mann test actions lol.

Could you do something like that these days?

I tend to think that if you couldn't you could get extremely close.

Also, for the billionth time foot pounds of energy is a trash metric for any sort of performance determination, stop using it.

Farmplinker

From: Farmplinker

11/1/23

TBF, some older ideas might actually work now with modern materials and manufacturing techniques. 

Although I think Emeric's neckless case experiment is more likely to work than the one in the OP.

smg762

From: smg762

11/1/23

ok ii've modified it. Total length is 67mm.   Scratch built case, with base diameter 8.3mm.  (wider than 5.7)

bullet is a 6.5mm FABRL, which is only 34mm long.  Case preassure 75k. 

could 1800 ft lbs be reached?

could you hollow out the base of the bullet to add more powder?

Also, could you squeeze in a .30caliber sabot, if the neck was extremely thin....  i feel this would be the boost needed to reach 1800ft lbs

  • Edited 11 January 2023 10:05  by  smg762
roguetechie

From: roguetechie

11/1/23

Emerics neckless brass case stuff is pretty exciting.

I do very much agree on older concepts becoming viable too. I think that our next round of material improvements is likely already possible and just waiting for someone to dust off an older concept that didn't work previously and update it.

On this note, Caleb crye's 5.56 or 300 bo feed through pistol grip concept is probably one of those things that just needs cleaned up and to have already existing innovation from outside the gun world applied to it to make it viable.

In reply toRe: msg 7
roguetechie

From: roguetechie

11/1/23

Why 6.5 fabrl?

Also when you scaled up bullet diameter you made sure to equally scale up projectile length with it right?

Otherwise your "6.5 fabrl" won't have the same performance characteristics your idea seems to need.

Gr1ff1th

From: Gr1ff1th

17/1/23

Gatnerd, do you mean QuickDesign or QuickLoad, because I have QuickLoad, send me the cartridge specs and I'll run them 

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