The owners manual says to use high velocity ammo. It also comes with two recoil springs. Find out which one is the lighter spring and use it with the hottest ammo (most expensive) you can find and it should work. Don't overlube it cause .22 is very dirty and it will gum it up in a short time.
I haven't had any trouble with magazines.
Agree with Firecop. My Mosquito fired CCI the best.
I did polish the feed ramp and it worked great. . Called Sig about having them look at it,but never sent it.
I have since sold it.