[weby]

Depends on what you want to do. Basically the short .50 bmg rifles are really not suitable for use as carbines, you need to use the rest.

As for building a suitable carbine doing more damage:
.50 beowulf from loadouts monster hunters is a good candidate, but below the 7d (6d+1 pi+), but if you use the optional bigger is better rules it gets the nice x1.8 multiple, so that compensates..
.450 Bushmaster is lower energy and smaller cartridge(only 1.6x multiple with bigger is better)
.45 Raptor is quite a lot higher energy, I wonder how well it can be shot without rest. But the damage profile would fit your criteria as it would be order of magnitude 7d+something of pi+ (though only 1.6x with bigger is better)

In something like .408 CheyTac or .416 Barrett you are talking around 11kj of energy and that is a lot to shoot from anything except a rest and the rifles for such tend to be pretty heavy too...

The heaviest cartridge I have shot from a short barrel is .338 lapua mag, and that is only about half the energy. An acquaintance has a shortened Sako TRG-42 and it shoots just fine without a rest and can be used well while standing. It is bolt lock though and still about 5kg, thus pretty heavy. A semiautomatic action would add further mass..

(The original short barrel TRG 42 model is 510mm (20"), but his is shortened close to the minimum allowed by law here, 400mm including the cartridge length, basically pretty close to half the barrel length of my long barrel version(690mm) and about 2/3 the original short barrel version.)


TLDR; If you use the bigger is better rules just use the .50 beowulf, if not, use as high energy .46/.46 as you can with your ST.