Picked up some used LE trade in mags, some are the older type that don't have metal liner on the front where the round feeds. I notice that the plastic is bulged out a little bit, will this affect feeding? Just got them for range mags anyway.
The first Glock mags were not metal lined and bulged when loaded which was intentional. When inserted in the gun and the mag release was accidentally hit the mag would not drop out which is a bad thing in battle. Remember these guns where originally developed for military use. This feature was not well liked by US shooters who are used to mags dropping free when the mag release is hit and Glock responded with the metal lined mags which do drop free. I've never had a problem with any of my original Glock mags. Some I've owned since 1986!
No issues with the older unlined mags, in fact I like them much better than the FML mags, they were designed to stay in the gun in case the mag release was hit by accident, a glock was intended to be a military weapon