Just got a box for my AGM MP40. Kinda disappointed. They don't fit well and I have to really jam it in for it to fire.
EDIT MUST READ!!
I solved the problem! It's kinda hard to explain, but I hope you get the jist of it... This is and easy fix: The angled lip that holds the BBs down inside the clip needs to be filed near the inside edge to make it a complete angle.
In the BB feed hole, there's an angle which leads to a flat plateau which causes the BB feed inside the gun to catch on it, instead of pushing it back, allowing the BBs to flow freely up into the chamber. Just scratch or file that plateau into an angle and it'll slide easier when you put the mag in.
I nearly destroyed 1 mag trying to figure out what it was getting hung up on! lol