First the M-4 that the military buys cost about half that amount. We use HK mags along other kinds of mags and they all have there good and bad points. As far as maintenance goes if you give the military a rifle that they know they have to clean less and they are going to neglect the rifle all together. And as for changing the caliber, chances are that is not going to happen because it's a money thing not only do you have to change the rifle but the mags and gear to support that rifle not to mention the M249 SAW. If anything they will eventually use 77gr bullets across the board instead of the 62gr bullet and that would be more logical.