hey, thank you so much for the feedback! I will be trying to revise these weapons.
AK74 is supposed to have less recoil and higher crit chance, but it may need some finetuning for it to be a late game weapon.
Winchester... well its a complicated case. Im trying to keep somewhat grounded in the real life weapons... but I will try to implement something to make it more useful. Maybe some levering attack. It does have access to subsonic rounds (only sniper with this). Also you can try to use the 7.62x54R modification. But still I will take a look at the base weapon
M82 probably needs AP reduction indeed

For M82 I would not get a reduction of AP. Instead I would give a builtin thermal scope (no out if sight penalty and no grazing hits) and a 200 damage (to make sure it kills a target if connects). That way you use 1 turn to set it up and you kill the target the next turn if it does not move.
Winchester is a semiautomatic rifle. You can just reduce the AP to 4 so that high agility mercs can get 2 aimed shots per turn. I bet it is also pretty light so the recoil should very light.
AK-74 has an ammo that has off blance center if gravity. When it hits an unprotected part of the bidy it causes massive damage. In game terms basically any hits on legs or arms should cause massive damage (high critical). It has very low armor penetration. Soviet Army replaced mist if them with AKMs by late eighties after the war in Afganistan as the ak-74 rounds were reflected of target by any tree branches it was touching on the way because of the round cobstruction.