I had several Suomi and Swedish "K" mags modified for my S&W M76 machine gun. So far 3 of the mags have worked and two have not. I still have one more to test. I was told that 124 grain (9 MM) ammo works best. I purchased a bunch of Winchester NATO 9 MM 124 grain ammo. I was told that other types of ammo might work better. I am open to any suggestions. Is there a "best" ammo for this gun? What about the mags? Will some mags just not work? Or are jams just more common with "open bolt" machine guns?