[lurkingknight]

if you can flip the gun upsidedown and gravity feed the tube.. put 3 or 4 in there and put light pressure in the tube so they don't fly out when you shoot... if it feeds find, the BBs are traveling up the feed tube just fine.

IF you have to force the BBs in, then you have an issue with the nozzle being too long or
the feed tube in the wrong position.

If everything drops in with minimal pressure then look at the BBs and the mags.

Load the mags, put it in a bag and flip the retainer.. if they spray out like a fountain, there's good pressure in the mag... If they sort of bubble out, there may not be enough force to push the BBs into the chamber fast enough.

Why you're experiencing some mags or some bbs causing the issue is that some bbs have better slickness to their polish and they slide against each other better than others. Secondly, the BB follower in the mag is sort of pushing the BBs off at odd angles, not directly along the chute.

If you can confirm it's a mag issue you can modify the follower to cup the BBs better and stagger the first 2 so they stack nicer and push upwards rather than be pushed outwards into the wall of the BB channel.