What Stealth said would be the best option but since you are in Alberta that will be a bit of a problem. My suggestion would be to find a local gun doc to diagnose the problem, this thread should help http://www.airsoftcanada.com/showthread.php?t=72809
A King Arms Colt M4 was my first rifle and it had it's share of feeding problems too. First thing would be to try better BB's, preferably BB Basterds. The biggest issue with mine was the magazine's BB retention tab, I had to file it a bit to improve feeding but every so often the same problem would arise. A new bucking seemed to be the solution to my problem.