VSSM Rebalance / New Gun Addition Suggestion
Right now, if you put the full auto attachment on VSSM, there is nothing else you can really do with the gun. This seems like a way to balance out the fact that you now have, what is basically, an SMG with a 1.8x headshot multiplier, but the real solution to this problem is so much better than removing the ability to customize the gun for one attachment.
Make the full auto VSSM a separate weapon, the AS Val, or, if you want a fictional name, the ASM (hey, that is what the 20p barrel is called, what a total coincidence), in the carbine category with a 1.4x headshot multiplier and no headshot-boosting ammo.
All that would be needed to do this is to copy-paste the full auto VSSM into carbines, lower its headshot multiplier to 1.4, change its name, remove the Match Grade and Tungsten Match rounds as carbines don't have those, add Standard FMJ rounds as the default 5-point ammo type, and then remove the full auto attachment from VSSM. Or, if you're happy with the current full auto VSSM balance, keep it, so people who don't mind sacrificing all their points on one attachment can still use it.
And, if you'd want to further differentiate the ASM from VSSM, on ASM make the ASM barrel and the OSA-7 sight default instead of the Factory and 1P86 LPVO, and on VSSM, make the 10-round magazine default instead of the 20-round magazine. Don't mess with the point price, the stat difference is enough of a balance, just make the 20-rounder unlockable instead of the 10-rounder, as it makes aesthetically (see Wikipedia photo of the two guns) and gameplay-wise (it's a DMR) more sense to start with a 10-rounder.
This way, we would get a new gun that would take near zero effort to make, as the model and stats are already done, and we could make proper builds with the ASM because its full auto would be balanced out by a lower headshot multiplier instead of the steep price of full auto.