Originally Posted by bamaranger
A full powered rifle cartridge in .40/10mm bore diameter, capable of launching 200 gr slugs to about 2250 fps. Think of it as a 10mm magnum, or a souped up " .40 carbine".
Think I'd base it on the .308 case, to take advantage of existing mags, bolt face dia's, etc. Don't know if the case is wide enough to offer a shoulder for headspace.
The rifle would be a short barreled semi-auto, based on Coopers "thumper" concept. NOt sure of platform but rugged and reliable.
So.... something like an AR-10, chambered in this: .400 THR Knockout
(aka "10x51mm THR") ?
DIY 40 caliber 225 gr bullet at 2,360 fps; or a 300 gr bullet at more than 2,000 fps
Be sure to check out page 2.
Though, I suspect you'd want just a little less body taper and a little more shoulder, for a semi-auto.