I got an ar-15 on a trade and the guy i got it from was an at home gunsmith... or so he thought. I had to have the gas tube replaced, a free float system removed, and I had to have the bolt repaired. I took it out to shoot it and the first few rounds shot fine. But then it quit feeding the rounds. I had to cock it every time i fired. Then sometimes it wouldn't catch the very back of the round and would jam. I'm thinking it's either the Mag or maybe the stock spring has too much tension behind it and wont allow the bolt to come all the way back to feed the next round.
Any other Ideas on what could be wrong?