I've got a Gen 4 G19 that came with three mags. I happened to pick up some old 9mm glock mags at the gun show. One was a 15 round gen 3 mag and the other is an old G17 mag. The G17 mag has no 9mm marking which lead me to believe it is really old but they are both factory mags. Also as I look on the side of the mag there is no beveling like you would find on the other mags I have. When I insert the old mag it tends to stick a little before being completely seated. I want to know if it's OK to use this old mag, to make sure it won't gouge my frame. I was thinking of sanding down the mag a little to make it more beveled. Thoughts?