For odd-ball conversions how about a M1 Carbine in .50AE or M14 in .338 Lapua. Both were tested in Guns & Weapons for Faw Enforcement some time ago. Both heavy recoil monsters, the .50AE recoil was enough to break the wood stock of the M1 Carbine. If you want real big, JD Jones makes a bolt action rifle that uses a necked down 12.7x99 case to fire a 20mm round. Rob