AMT, Automag III .30 Carbine

[vtjpm]

I don't know if this has been covered before. I have an AMT Automag III .30 carbine. It seldom feeds the last round, and if it does I get a misfire. I sent it back to AMT several times. (last time in 1993) Any ideas on how to fix this? I've used new mags with no luck. Thanks VTJPM