I run 5x 120 rd. midcaps, usually loaded to around 75-90 rds. each.
But as for the original question I've used that exact gun you have before (borrowed it). IIRC it did take STANAG mags HOWEVER they were slightly different from my regular STANAG mags for my M4. IIRC the biggest thing I noticed was the lack of the rear "bump" on the FAMAS mag while my M4 mags had that bump, also where the magcatch actuates (ie., on the side for an AR but on the front for a FAMAS).
ಠ_ಠLess QQ more Pew Pew
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