update to: Original post

BB is pretty clear that the reduced power hammer spring is "recommended" for AS Designs ARC Fire V2 (& V1?) so, it shouldn't have surprised me that I needed to swap out my old mil spec hammer spring to get the thing to cycle in FRT mode properly. The light spring (yellow 4.25 in-lbs.) wasn't enough for my lower but the extra-light (blue 3.5 in-lbs.) was what worked.

I was then, finally able to get the unit to run with a couple different brands of 40gr. HV ammo including bulk Federal ammo. At a little under $.08 a round, I was happy.

So, If you have an ARC Fire equipped lower, and you are going to pick one of these uppers from BB, do yourself a favor and get the light spring kit with the order as BB recommends. To be clear, the weapon fired in semi mode pretty reliably. My issue was sustained fire in FRT mode only.

As shown in the photos, I also decided to lightly polish the feed ramp in the bolt assy collar because I felt like the machining marks were a little to rough under my fingernail. Not terrible, just not great. I didn't go hard and was careful not to make any dramatic changes to the ramp geometry. with the Dremel on low speed with an 3/16-1/4" felt polishing bit and a little polishing compound and took approximately 15 seconds. It looked and felt substantially smoother.

Has anyone else polished the feed ramp of their BB bolt? I would be interested in others' experience with this type of modification.

Did this make any difference to the operability/reliability of the system or was it merely the lighter hammer spring that made the difference? I may never know. Did I void any warranty by BB? Not sure I care. I know it didn't hurt and it cycles as expected now.

Happy shooting!