My Black Aces (BA) receivers came in this week. Picked them up when I got home from deer hunting on Wed. Put one together from parts from a donor shotgun this morning.
The receiver comes with a bolt, carrier, mag release, and extended firing pin. It is about an inch longer than a stock Mossberg 500 receiver. You need to pull the firing pin and bolt block out of the stock bolt and install them into the BA bolt.
Because you aren't using the tube mag you do not need the shell stops, lifter, mag spring or follower.
You do need the mag tube, barrel, slide/grip, trigger group/cross pin, and ejector.
As noted earlier at least one of these is intended to be built as a short barrel, smooth bore firearm that is just over 26" OAL so that no SBS or AOW registration is necessary. My intent is to have one with a Shockwave Birdshead grip and 14" bbl and the other one possibly will have a shorter bbl (probably 9 or 10") with a buffer tube and Sig Brace on it to bring the OAL back up to 26". All of those things are on order.
They had three colors, black, green and gold. I ordered the black and green. Somehow got a gold one instead of a green one. Oh well. Shown with an 18" bbl off my other Mossberg but am looking for another cheap barrel to cut down.
Shown with a stock 5 round Saiga mag, but my 10 rounders will fit and hand cycle shells. The drum will seat though I can't get them to hand cycle shells through it yet.