Built it in 98 from a Saiga 410. Bought it for conversion and never had a shotshell in it. The barrel is threaded into the trunnion not pressed like most AKs and made the custom gas block with tungsten carbide piston. Built like a M14 gas system as the piston and op rod are separate pieces. Barrel blank was purchased from Green Mountain barrels. I did 100% of the machining, welding and cussing. If you. Google search Saiga 500S&W conversion it will come up on a few forums and was first posted on the AKFORUM. More details are available on GUNCO.
Cost per round? About the same as other large calibers. I reload. Usual load is 385 gr CLHP @ 2000 fps roughly 3400 ft ke.