When i have a problem with a magazine not feeding, I pop out the follower and take a dremel to it so that its stepped much liked a real steel mag follower. Worked for my g&p midcap which refused to feed any bb, no matter the quality.
http://forums.airsoftmechanics.com/index.php/topic,5655.0.html
http://forums.airsoftmechanics.com/index.php/topic,5655.0.html