For accuracy, it isn't too bad:

... and I was in less than top form off the bench. Just couldn't get settled in. Lack of gun weight is probably a contributing factor. Still, .21" on centers is nothing to sneeze at. Grandson did take a couple of jack/snow-shoe rabbits with this bbl and the 16 gr polymag predators at 15 pumps. He was well this side of 20 yds for both.
I couldn't quite see 600 fps with the 18.1 gr. JSB Heavy pellets. 575.4 avg at 25 pumps. This is where this particular build tops out~ going to 30 pumps only yields an increase of 10 fps. Interestingly, with these pellets, the narrowest strings occur at 15 pumps with a max deviation of 7.3 fps, and an average of 536.7.
The valve in this build is an old 22-89 valve with the bleed vent plugged.
I'm going to have to compare the milling on the bottom of the home made hammer with a P-Rod hammer. I may be able to relieve a bit more there, if memory serves me right.
I think for the up coming 2200 conversion, I'll use the 24" bbl. It's a bit faster at top end of a 13 series gun, and accuracy is a shade better. I'll leave this little carbine as is.
-D.S.