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.

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

in terms of handling high pressures, aren't big game cartridges often straight walled?

would such a cartridge extract realiably?

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.

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

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.

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. 

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.

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

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.