The MK-48 is described as:
An LMG that dishes out heaps of damage.
It’s located in eastern Espiritu Santo province, at a hotel with a cartel presence. The weapons case is outside, at the back of one of the hotel buildings on the west side.
This approach was a mess for me. The surrounding area is jungle, so I would suggest circumnavigating the enemies and approaching through the jungle from the west. I ended up going in guns blazing because we were spotted and my team mates all got taken down, so try to be tactical and stick together.
The description here is a bit deceptive, because the damage rating for the MK-48 is really middle-of-the-road for LMGs, but does combine with the highest rate of fire in the LMG class. If you want to deal the most damage with an LMG the 6P41 found in Media Luna is the real heavy hitter. But in all honesty, all the LMGs do noticably more damage than the other automatic weapons in the game.
Regardless of this, the MK-48 does stand out as being the only LMG to take an extended magazine. It has a 100 round standard box magazine, and a whopping 200 round extended magazine is available in Inca Camina.