Yeah...
Back in the day, when I was an admin on the Detroit Mux had a player who wanted to mount a sniper rifle on their drone. That idea turned into a STD with the riggers "I wanna sniper rifle in the turret of my bulldog."
Unofficially,
I have always believed that the high damage value of the sniper rifles was due to precise placement of the bullet through the target's eyeball (doing an end run past the target's armor). As such, I would not allow the player to do called shots or even aiming. They seem redundant, to me, given the damage value of the weapon in question. Kind of like, "do I get a bonus for exhaling (holding my breath) and squeezing the trigger instead of jerking it?"
HMG's have burst fire and full auto mode so that levels the playing field (literally).
There are barrels and then there are -barrels-. Sniper rifles boast accuracy of 1/4 MOA something that any machine gun (light, medium or heavy) simply can't claim. It might help to think of machine guns as area denial weapons, you go into their field of fire and you are denied life. Sniper rifles are on the other hand are high value target weapons, snipers are trained to target officers, radio men, machine gunners, exposed tank commanders, etc..
Once you get into the .50 BMG range, technically those are anti-material rifles (and about as much fun to shoot as being hit by Mike Tyson).