[Zack The Ripper]

I second under filling the mags. If they hold 120, fill them with 90 and see what happens. I have several mags that I have to do this to with my modded M4 as the spring tension in the mags is too high.

Should this technique work, them it is likely the spring tension is too high. If this is the case, you can try filling the mags to capacity and leaving them filled for five days or even more. This extended compression of the spring follower should allow some of the tension to release and should help with feeding. This does not always work though. Again, test the above mentioned method out of only filling the mags 75-80% and see what happens, then go from there.

Also, be sure your hop up is very clean inside and out, and ensure there isn't an excess of lube. This will be detrimental to feeding as well as proper air compression when firing.