When I was issued an M4, the standard load out was 210 rounds. 6 mags on your IBA or belt, and one in the rifle.
When I got certified as a SDM (squad designated marksman) I carried 6 20 round mags (to used with a bipod) and I carried an extra 4 30 rounders of my accord.
When I was on breaching duty, the 590 stayed loaded with buckshot, except for the round, which I kept loaded with a M1300 (1330? I cant remember the number) breaching slug. Halfway through, they made us switch from buckshot to slugs though.
Always kept 5 mags for my M9 (if I had one) 4 on the belt/IBA, one in the pistol.
Korey - Shamrock Armory
Glaine ár gcroí, Neart ár ngéag, Beart de réir ár mbriathar.
Purity of heart, strength of arms, and truth in words.