This is how I would change the Constitution

I would buff the damage to 280-330 and keep its penetration at AP3. Other improvements would be changing the irons to a ladder sight (or something better than the one we have) and/or adding a medium-range canted scope like the type 38 on image 4.

A different change would be buffing the damage to 300-350 (also at AP3) and giving it a long-range scope and moving it to the sniper class instead of marksman.