Sig P228R - Factory Mags x2 (13 rds)
Glock 30 - Factory Mags x2 (10 rds)
Stag-15 - Factory Mag x1 (10 rds) Magpul Mags x3 (30rds)
In other words...not enough...
Generally I would like to carry one mag in the weapon + 2 in a mag carrier.
The exception being my Stag -15, where if I have to worry about carrying mags something has gone HORRIBLY wrong, and if that's the case my vest can accomodate 8 30rd magazines.