The problem with .311 bores is that they do not shoot .308 bullets accurately. .311 bullets are typically only found in weights up to 180gr, which is more difficult to run at subsonic speeds in the 7.62×39mm case. The largest advantage of the 7.62mm Thumper is that the underlying case is common and, unlike most , does not require modifications for subsonic loadings. Also, when loaded with heavier bullets it employs enough propellant to reliably cycle gas-operated semiautomatic firearms designed for the 7.62×39mm.