I had thermolds a few months back and went to the the range. it would shoot once then fail to chamber a round. it would get stuck halfway between the mag top and the feed ramps. got new CMMG chrome silicone mag springs and fixed the problem except for having to load one less round so it would cycle because it would only cycle 29 properly. Here s the strange part: I bought new Aluminum Labell mags from lauer. took the  chrome silicone springs out of my thermolds and put them into the Aluminum ones PLUS added magpul self leveling followers. figured I would have absolutely no problems. HOW WRONG I WAS!!! The same malfunction occured using the aluminum mags. is this  a gun problem or a mag problem? All of the components of the magazine are  brand new. I DESPERATELY need someones advice on how to fix this issue once and for all. As it makes going to the range, a profound dissappointment , but I really I like shooting the gun when it works.

Here's my gun description.

Colt Upper
Bushy lower
Bushy 14.5 inch M4 profile barrel

Tighten up you mag catch.

The problem would be the magazines, not the rifle.  Buy Okay or Parsons (I think it was bought and has a new name now).  I don't particulary trust plastic mags.  I had a "Thermelt" and gave me problems. I ended up destroying it.  Went back to Okay, Parsons, and Armed Forces of the Philippines issued mags.  No problems.  Keep them as stock as possible.  Modifying them will just give you problems.