This is a discussion on Mags won't stay in within the Ammunition forums, part of the M14 M1A Forum category; One of my M14s won't reliably keep the mags in place. It seems that the mags are OK (all USGI) since my two M1As hold ...
First you need to figure out why the mags are not locking in.
1. It could be that the mag release/lock is defective
2. Could be that the mag well is to tight for the mags to go in all the way and lock.
3. could be a worn oprod spring guide.
4. Are you inserting the mag on a closed bolt and the mags are loaded? (can be done but a bit more pressure required).