The feed springs (stock) are pure poo, and I mean that in the most positive sense.
The #$%#& stock springs have shaped ends, so they stay put in the plastic clamp areas. They DO stay put- quite well.
But I had to tap, tug, pull, push, hit, thwap, (insert favorite onomatopoeia) or otherwise BRIBE good ammo to feed on a regular basis.
Seems the problem is that the BB's can stack off-center when they enter the stock feed spring, and get hung up in those little grooves between coils. Going to a spring made of tinier wire means smaller grooves.
Mine works VERY smoothly now (for an A&K magazine, let's be REAL about this).