Q-BRANCH (of the GURPS forum)

[Icelander]

Originally Posted by Donny Brook

Here's one you may enjoy:

The CQB Stormer is designed to pack serious punch, throwing heavy lead in high volumes. This weapon is based on the Springfield M14, then converted to bullpup configuration to improve bulk, accurized one step, incorporating two accessory rails, and rebuilt to fire duplex rounds based on the Marlin .444 cartridge (which was chosen to provide large calibre stopping power with muzzle energy not too much more than 7.62 NATO thereby retaining similar controllability during autofire). The larger action lowers the RoF, slightly, but this is more than compensated by the use of duplex ammo.

TL . . Weapon . . . . . . Damage . . . . Acc . . . . Range . . . . Wt . . . . . . . . . . . RoF . . Shots . . . . . ST . . . Bulk . . . Rcl . . . Cost
8 . . CQB STORMER . .. . 6D-1 pi+ . . . 6 . . . . . 225/1450 . . 10.049 /1.144 . .. 10x2 . . 20+1 (3) . . . 11 . . . -4 . . . . 3 . . . 1550 /79.04

Chambering a .308 rifle for a rimless version of the .444 Marlin is not a bad idea and has even been done in real life. Of course, there is no compelling reason to actually base this weapon on the M14, but that's a matter of flavour more than actual mechanics. It would probably be more suitable for flavour to use an AR-10/AR308/DPMS as the basis for the build, or possibly steal the name of some cool and futuristic-looking bullpup like the Desert Tech MDR and just note that it's a variant chambered for the fictional .444 cartridge you're using.

Personally, I'd use Douglas Cole's spreadsheet to calculate the actual Wound Channel Modifier of the smaller duplex rounds rather than just use the nominal caliber, as it's probably unrealistic for ca 120 grain duplex projectiles to have a higher wounding modifier than 300 grain .338 Lapua Magnum rounds, but I'm aware that not reducing the damage type is technically RAW.