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.

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.

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

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.

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.