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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; 2151 views.
Farmplinker

From: Farmplinker

30/1/23

Er, no. The straight-wall cases are for lower pressure rounds, generally. Those Nitro Express cartridges were big to keep pressures low enough for break-open rifles.

smg762

From: smg762

30/3/23

emeric i had a question...

i've modified the parameters of the round - it's now much more powerful.

caliber is .25, so the bullet diameter is 6.49mm (not 6.7mm)

ME is 2100ft lbs - similar to a hot 6mm cartridge

base diameter is much wider now - but still far slimmer than typical 6.5mm rounds

it's 9.85mm - slightly wider than 556.

case is about 49mm tall, and the CETME bullet is almost entirely outside the case - there's about 4-5mm of bullet in the neck.

do you think it would work, and would it reach the target energy?

and i wanted the bullet to be entirely hardened steel. could such a bullet reach a reasonable weight?  idieally 95 grains

EmericD

From: EmericD

30/3/23

smg762 said:

case is about 49mm tall, and the CETME bullet is almost entirely outside the case - there's about 4-5mm of bullet in the neck.

So, you want to use a flat-base bullet? I tested recently a 5.56 mm flat-base bullet that flew very well.

Scaled up to .257" cal, the bullet caracteristics would be:

  • 32.6 mm length, 22.4 mm ogive, 0.85 mm meplat.
  • 92 gr steel bullet and a C7 of 0.207.

You will need to run at a very high pressure to reach 970 m/s and 2800 J of muzzle energy.

A 49 mm case + a 32.6 mm bullet length - 5 mm of bullet intrusion = 76.6 mm cartridge.

smg762

From: smg762

30/3/23

i was hoping for an extremely long CETME bullet - 36mm. 

apparently the 556 FABRl was 31mm so a .25 bullet should stretch to 36mm?

i'm aware the round would be very long - more than 762 NATO

assuming a CETME or FABRL shape, i feel that a 93 grain bullet would have a very high BC.

the 7.92 CETME was 105grain, and apparently had a similar BC to 762 NATO. 

EmericD

From: EmericD

30/3/23

smg762 said:

apparently the 556 FABRl was 31mm so a .25 bullet should stretch to 36mm?

The L/D of the initial FABRL was 5.5 (https://apps.dtic.mil/sti/pdfs/AD0765459.pdf ; p.13) but it seems that they reduced the bullets length during the tests at 4.73 (https://apps.dtic.mil/sti/pdfs/ADA039156.pdf ; p.80).

So, depending on your taste, the .257" bullet could be 1.216" (30.9 mm) to 1.414" (35.9 mm) in length, with an ogive between 69% and 73% of the overall bullet.

A steel bullet with an AR2 shape is reported to have a weight of 5.372 g (82 grs) here https://apps.dtic.mil/sti/pdfs/AD0882117.pdf ; p.191 and +, with a mean BC around 0.201.

smg762

From: smg762

31/3/23

what was the caliber and length of this bullet? was it entirely hardened steel?

i feel a 93grain bullet which is 36mm and all-steel would have very high penetration at 3000fps velocity

In reply toRe: msg 1
Mr. T (MrT4)

From: Mr. T (MrT4)

31/3/23

By the way what was the problem with  .224 Boz 

On paper a cartridge that could be used in existing guns seemed to be the ticket.

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