What...problem are you having ?? Don't understand. The magazine to gun fit on my LP50 is excellent.
Just make sure that the magazine rotation is correct, before you try to insert it. The magazine slides right in place...a square magazine...into a...square hole. What else do you need. The pellets DO...need to be FULLY...incapsulated by the magazine. They CANNOT, stick out of either end of the hole that they rest in. This pretty much limits you to using only..."flat" head, or wad-cutter pellets.
And yeah, that $75 price is WAY outta line. The machine shop probably makes 10 at a time, on a CNC mill, with two, maybe three setups. The magazines should cost about $10 to $12 ea. !!
Mike