I just solved the problem in my Beta project AK mags (PTS mags)
These would never reliably feed especially when filled to the 140 rd capacity.
They have the hinged followers with the rounded point that jams up against the side and the other BB's periodically.
What I did was really easy to fix and I just tested it with 7 different full mags on a 40RPS AK.
It fed flawlessly the entire mag, no misfeeds at all, where there would usually be many until the mag was at least half empty.
All I did was take a soldering iron with a round tip, approximately the same size as a BB.
I pulled the follower up through the BB release catch so that the tip was caught above the BB release lip.
I then pressed the heated solder tip into the centre of the follower and melted it until there was a round indentation that would solidly cup the bottom of a BB. This way the follower never moves off the bottom bb or slides around causing a jam.
I was extremely surprised, whole mag, 140 rounds non stop to the very last BB on full auto, not one problem with .30 BB's. And it can all be done without taking the whole mag apart.
Give it a try, I know these mags are going back into regular use for me now, they sat in the bag before because they did not feed reliably.