My thinking was that since he keeps his magazines loaded all the time the spring will take a set and actually not be as strong as it should be if he were shooting it on a regular basis.
He also said that he checked the feed lips and they were not flared which let me to suggesting stronger springs.
I would be worth trying before he started messing with his gun.
I do see where you are coming from too though.
At least we both agree that it is the magazine and he should get new ones or at least new springs.[8D]