I assume this is what you mean by m249. From the usmg.pbo readme:
=======================
Weapons:
=======================
M249 SAW : otwM249MG
M249 Para : otwM249paraMG
M249 PIP : otwM249pipMG
M249 SPW : otwM249spwMG
M249 Para Scope : otwM249paraScopeMG
M249 PIP Scope : otwM249pipScopeMG
M249 SPW Scope : otwM249spwScopeMG
M249 SPW Red Dot MG (red dot aim scope) : otwM249spwRedDotMG
M240 : otwM240MG
M240scope : otwm240scopeMG
=======================
Magazines:
=======================
M249 Magazines : otwM249Mag
M240 Magazines : otwM240Mag
=======================
Units:
=======================
otwM249sawSoldier
otwM249paraSoldier
otwM249pipSoldier
otwM249spwSoldier
otwM249paraScopeSoldier
otwM249pipScopeSoldier
otwM249spwScopeSoldier
otwM249spwRedDotSoldier
otwM240Soldier
otwM240scopeSoldier
=======================
The otw M1911 is "otwm1911a1" and "otwm1911a1mag."
the glocks are "otwglock17" and "otwglock18." Just add "mag" to the end.
The originals are "cz75," "glock," "beretta," and "tokarev."
I don't know the rest. haven't even seen the G3 yet. Which soldier has it?