Sounds like my old gun. Sold it 5 years or so ago. I never shot it much, maybe 50-70 rnds. Liked the 140 Sierra's. Shot a 4"-5 shot group @ 600 first try. Nobby Uno built, can't remember the bbl make, probably a Hart. That's what Nobby likes. should be a 8 twist. Had the muzzle brake copied from a KDF and made by a local machinist. It screws on, the bead blasting hides the join. It worked good. BBl was broken in properly, 1 shot clean, to 5 shots, then 2 shots & clean to 10 shots, then 3 shots & clean for another 9.
I started shooting 6 ppc's and 6 br's more so I sold it.
cheers