[COSteve]

How are you chambering the first rd? Do you pull the charging handle all the way to the rear and let it go or do you 'ride' the handle forward? If you aren't pulling it all the way to the rear and then letting it go, it's likely your problem. If you are cycling them correctly, then the fault is very likely the mags; seating too high, the follower too high, them dirty, dented, or rough inside so the followers aren't pushing the rd into position correctly.

The system is meant to function with the full force of the cycle, not being 'babied' into place. Many shooters think they'll hurt their rifles by allowing them to cycle forcefully, however, that's exactly how they were designed to function and easing them into place will actually increase the likelihood of a malfunction.

Back in the 60's we taught the 'cruits' in the Army to jack the charging handle back firmly and let it go, then tap it forward to make sure the first rd was seated and the bolt completely closed. We taught them to "rack and tap" the charging handle to make sure the action was fully closed. We also made sure that they cleaned their mags when they cleaned their rifles to ensure the the whole system functioned smoothly. I do that today on my M1 Garands, M1A, M1 Carbines, and my Mini-14; all from the habits I learned in the Army and as a result never have an issue of the bolt not fully cycling.