The overall length for a given barrel length would be much improved as you would have no action length.

https://www.forgottenweapons.com/the...le-for-the-ss/

Think of something like this in .50 BMG. Heck, even something scaled down & lightened in .300 Win. Mag.

IF and that is an IF the design would work with a double feed position mag, make it in .300 BLK using AR mags!!

TED