What would cause this failure to feed?

[imntxs554]

I've had this problem before on one of my Carbines and i just almost yanked all my hair out trying to figure out what was happening. One thing that did help I loaded only 14 Rounds and see how it fed from the left side of the mag and it started to work, but I knew there was still a problem. I even inspected the face of the Bolt just to see to see if there was anything wrong. If you can't find out the problem with what Jim or Bonnie just recommended I did finally find out what it was, but I had to do a little something not really what you should do, but I did it and it has worked ever since. I'll just wait to tell you after you tried everything first. I would have to take pictures and mark where the problem was. My friend came by to visit and i told him what im dealing with and he looked it over and fixed it in less than 10 minutes it's requires using a small ball pin hammer.