As SteelCap says, LAR and Beo mags are fine...5 rounds is the max you can load per mag. The course of fire for a match is 88 rifle and 22 pistol (bring double this amount of ammo as we do a practice round in the morning - reload mags over lunch). Mostly you will have 4 x 5 Rd rifle mags and 2 x 3 Rd pistol mags as your load out for each relay. Two relays require an additional 4 round rifle mag and the last relay, your 2 pistol mags are loaded to 5 rounds. So, be able to carry a max load out of 5 rifle mags and 2 pistol mags...chest rig, plate carrier, vest, battle belt, big pockets, whatever...I've seen all of the above used successfully at a match.
I have some LAR and Beo mags that I use in addition to standard USGI mags, just make sure you can grab them quickly from your pouches...this game is about quick reloads. I have GS Designs extensions on my LAR / Beo mags so they are the same size as the USGI and stick out above the top of my tacos.
