Pretty straight forward. It has better ballistic cooldown than the 3C so it's a natural choice for running an AC5 combination for the DPS. It fits very well with the XL255 and plenty enough ammo. Alternately you can drop some ammo for backup weapons.
This became my go-to Rifleman (I somehow can't stand the other versions), albeit with the stock engine. The latter seems to be fairly sufficient and allows for another half a ton of AC ammo, upping the damage potential from the ACs alone to more than 1k. Double MLas for backup & close range seem to be somewhat obligatory to me.
4/5, Nice DPS thanks to the ballistic cooldown and sufficient range for not being caught in a desastrous infight. I especially like this one on the hot FP maps as a medium / long range suppression build.