Don't get the Heavy though! They're proprietary mags!!! The mags are pricey and only the VFC ones work.
Go for the light they take the standard TM mags. If you're part of a unit and run out of ammo anyone with a standard M4 can toss you a mag and you're back up... The VFC heavy... you're SOL or need to go to your secondary.
“We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm.”
To those Rough men... Thank You.