So the m249 is fine. But the other ones have a severe lack of ammo and as gunner you simply can't do your job to keep suppressing and defending. Also is it extremely annoying and frustrating to run back and resupply, while enemies are still pushing.
The only purpose these guns are good for is pure defense and you can't do that without enough ammo. Any other option than fully maxing out your ammo capacity is a no-go for the gunner. The lighter weight and more mobility argument doesn't hold up either, when trying play a mobile suppression role you stand no chance in pvp.
Non-extended mags are just a no-go, because how is 150 rounds with heavy carrier enough for the m240b & mg3? (vs 600 rounds of the m249). Neither is extended mags + light carrier enough, 200 rounds still is peanuts. But even with 300 rounds you run into the problem described above.
The whole ammo model and choices for the gunner is just insufficient and also uninteresting, since maxing out is the only option. So I've puzzled around a bit with supply points and ammo counts and I think I've found an interesting model:
PKM (5 instead of 3 supply points)
- No carrier:⠀⠀⠀⠀2x 100 (come on, who ran 1x100mag before?)
- Light carrier:⠀⠀⠀3x 100 (5+1= 6 points , same cost+ammo as heavy carrier originally)
- Heavy carrier:⠀⠀4x 100 (5+3= 8 points)
MG3/M240B (6 instead of 4 supply points)
- No carrier:⠀⠀⠀⠀2x 50 (1x 50 is a total utter joke).
- Light carrier:⠀⠀⠀3x 50 (6+1=7 points, same cost+ammo as heavy carrier before)
- Heavy carrier:⠀⠀5x 50 (6+3=9, 50 rounds less than heavy carrier + extended mags originally, but also 1 point less)
Extended mags (keep 3 supply points):
- No carrier:⠀⠀⠀⠀2x 100 (6+3=9 points, nobody even ever chose 1x100 before)
- Light carrier:⠀⠀⠀3x 100 (6+1+3=10 points, same ammo+cost as original heavy carrier)
- Heavy carrier:⠀⠀4x 100 (6+3+3=12 points, 3 point left to spend hehe, still balanced right?)
M249 keep all original?
Seems all balanced.
The weight of extra mags should be counted, otherwise it's a double buff of more ammo+lighter weight. Is not what we're trying to achieve.