Mis feeds can be caused by allot of things.
You didn't say what type of rifle it is (Chicom, Yugo?),
I have heard that new Tapco mags sometimes have
some flashing from the molding process.
Take the mag apart and make sure there is nothing preventing
the follower from sliding smoothly.
Also at the feed lips, sharp corners may need a little sanding etc.
You'll know more after you test the factory mag to see if it runs with that.
Most misfeeds have to do with the magazine.
Correct angle, feed lips and tightness inside the action.
Keep us posted.