With US made plastic mags it's fairly common to have to file fit the mags to the gun. Not hard to do. Look at where they bind and just file a small amount of the mag away at those points.
It's best to do it when the gun is field stripped because one place they hit is sometimes the center support. That's the collared pin that the hammer rests against when it's down and the bolt and carrier are removed. You can't see it hitting if the gun is assembled, but when it's stripped it is pretty obvious.
