1. It is a bit unusual to have someone that owns a firearm worth several thousand dollars, but does not know how to field strip it. Last M2 I saw was about $6,000. Hence the question.
2. The gas piston in the US Carbines can be removed. But if you do not have a bit of armorer's equipment called a Gas Pistol Tool, you will NOT get it back in. Was not made to be user removable.
3. Bad magazine, or bent mag lips may be the problem. What ammo are you shooting? And which mag- small, medium, or large?