I would contact the issuing agency to see if they are having a rash of complaints about the ammo. In my personal experience with AMVET or similar M1 Garands is that they are typically worn out and poorly maintained - as in they have received zero maintenance for many years. Without a hands-on examination of the rifles, it is impossible to troubleshoot them. You could try running a few rounds into a stripped small base sizing die, but I would start with a small quantity then test fire them.

I expect that your problem is more likely gun-related, than ammo-related.