It could be the low quality of the BB's itself.
I had tried some low quality .25's in my M4 and although they did not have seams or anything really sucked and wouldn't feed properly in my gun. I however have had success with BB Bastard, MetalTech, Madbull, and BB King.
EDIT: Oiling the mag might help as may removing the feeding spring and stretching it out (giving the spring more "push" in the mag to actually push the BB's out).
Since silicone oil is safe for rubber your hop-up should be fine but you don't want anything on your hopup (or it isn't as effective) so after doing the oiling thing feed some BB's in and just eject them out by hand, in addition just to be safe run a cleaning rod with a cloth on the end of it through your barrel. HTH.
ಠ_ಠLess QQ more Pew Pew
READY TO >> RACE
Last edited by L473ncy; August 8th, 2009 at 12:26..