CYMA Ak 74u with the following upgrades:g&g bearing spring guideSHS Al cylinder head (teflon taped, mouse pad foam used to correct AoE.)Systema bucking ( internals removed, roteted 90*, whiped with dental floss)g&p explosive piston head (O-ring expanded)SHS PistonDeans plugs9.6v 2/3 amp elite batteryMadbull m120O-ring nozzle of unknown brand ( slightly shortened, it was to long)Also the usual diy mods: Barrel spacered with e-tape. Reshimed/relubed. Tappet plate sanded. Cylinder polished.16 rps, 404 +/- 2 fps, 14" grouping at 180 feet. at last measurement.