The difference in damage is in place to make the experience more enjoyable, if every weapon done the same damage it would fucking suck, G3 is one of those guns that imo are there to be used strategically as with some situations it works better than in other situations, But that's the same with most guns, G3 can't be used very well in gunfights, Shotguns can't be used in long range fights, Snipers don't always work very well in close range, Pistols... well are pistols.
One of those guns that I think are just meant to be shit, Buff it and it gets OP, nerf it and it gets shit, Not sure if there is that one perfect balance.
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