Easy way to nerf all the op guns without "nerfing" them.
Increase health.
Buff all guns, with the lesser guns gaining more improvements.
Example (dramatized to demonstrate the concept, not suggest a planned improvement):
Max Health: 75
Bar: 10 base damage, no changes to other stats
M4: 9 base damage, no changes to other stats
Famas: 8 base damage, higher rate of fire, increased spread
Handgun: 7 base damage, increased spread (even more spread dual wield)
Current Hits to Kill: (Bar)6:13(Handgun)
Example Changes: (Bar)8:11(Handgun)
Not all guns would receive damage buffs (ie Famas) to add variety and help disguise the nerfs.