LMG

A portable, high-capacity, high rate of fire machine gun, typically very heavy and mounted on the ground or on a military vehicle. They are typically fed ammo through a belt or large-capacity drum magazine, and are used for suppressive fire rather than targeting enemies.

“That LMG has some kick!”

“Yeah, I know, and it has 100 rounds!”

LMG

Abbreviation of light machine gun
Big In video games (call of duty etc)
Usually a type of machine gun but well lighter

“He has a lmg! Run!”
“Provide cover fire with that lmg you got”