Heavy Machinegun is a weapon upgrade to Machinegun. It can be picked up on any map.
INFO
The Heavy Machinegun ups the firerate and damage over the starting variety, but the same properties still apply. Compared to the Lightning Gun, the spread on the HMG allows for a little more leniency in aiming in exchange for lower damage, but with the added ability of being able to return fire against champions holding the Railgun.
A Quake 3 Machinegun skin is obtainable via loot boxes, shards or hard currency.