Shi_Huang_Di, welcome to the boards. What is the significance of your name?
No shame in having a Century L1A1, with a little TLC and maybe some parts swapping you can convince them to run 100% reliable, for very little money. Bring it to the shoot and Mousegun and I can help you diagnose your problem. In the meantime, try to find "inch" magazines to use in your "inch" receiver, "metric" mags can be used in an emergency but, as you have discovered, they often will have feeding and fitment problems.
METALMAN, I believe that most of the Chinese Kalashnikov variants had holes in the gas tube for a couple of different reasons, namely cyclic rate control and heat dissipation. Most European variants do not have these holes, and drilling your own on a European gun would probably be a bad idea, since the gas block and gas port are different.
Bring gloves for bumpfiring my drum mag--and I hope you don't mind melting that lower handguard just a bit.