There is no military designation of 'M1A' for the M14 rifle. It's still an M14 without the selector switch, just set for Semi. It would be the same if they took some M16s and blocked the switch from going auto. It's still an M16, not an AR15. 'M1A' is the strictly Springfield designation for their civilian M14-style rifle. Your points about different ammo for the M16/M4 causing supply problems is valid. The military has always depended heavily on standardization of all weapons and ammo, so these very problems would not occur among the majority of field units. Testing is always going on in combat theatres, and certain special units will get the new equipment for evaluation. These units will be specially supplied so incompatible equipment/ammo does not get into the normal supply chain. Could this cause problems with those units? Absolutely. If their ammo truck gets whacked on the way up, they could be in a world of shit. Any combat situation is regarded as an opportunity to try new things in field conditions, and as a training opportunity for personnel. I'd say that out military right now has the most experience in today's urban combat in the world, and this is a huge factor in the scheming of those who would oppose us.