AK Hi-Cap issue

I got a CYMA CM031 and the Mag that came with it will only cycle ~10 shots before it will dry fire and then I have to hold it upside down. My midcap is only 100 rounds and is broken, so I need to figure out a fix. It's not the gun, because before the midcap broke it shot fine with it. The mag wobbles in the gun, but I don't think that's the issue because when I do fire off a few shots and take out the mag I can't see BBs in the top, but when I tilt the magazine upside down the BBs show up. How do I get the spring to work again? It's my only AEG and I'm playing tommorow so I need a fix pretty quickly. Any help would be appreciated!