I use a chest rig. I run a smallish dumper right on the front at the bottom in the centre like a groin protector almost. I can reach it easy no mater what hand im shootin with and with the m4 i can literally just eject the empty mag right into the dumper while grabbin a fresh mag with the other hand. Been thinkin of movin it to a drop leg on the left or around back but that would either defeat the ampi use or cause the reach around that takes extra time and also would probably make it hard to keep engaging targets while reaching for it.
The downside is cant get at it so easy when prone then i just leave mags n pic em up after when i stand or kneel.
Pardon my crppy bedroom pic lol