I've shot a fair number of lots of SK Std+ over the past several years; never got very serious about lot testing it because I figured there'd always be a fair number of flyers with ammo in that price range. However, I decided to buy some lot samples of it a couple of months ago, and wound up finding a lot that had far fewer flyers than any other Std+ I'd ever shot. I thought it was good enough to buy a case of the stuff, so now I've got some pretty good ammo for fun shooting, not just in the 40XB & V-22s, but also the two CZ 457s I've got. I'm somewhat more than slightly surprised that the same ammo that shoots well out of ACE, Bartlein, Krieger, and Lilja custom bbls also shoots great out of a CZ 457 MTR, which has a much tighter bore than even the Lilja titebore bbl on my 40XB. Not sure why CZ goes with this tight of a bore diameter on their hammer forged .22RF bbls, but with the tighter match chamber of the MTR, that bbl shoots very nearly as well as the customs do.
OTOH, the factory bbl of the 457 American has proven itself lacking in consistent performance - unless you consider consistently poor accuracy 'consistent'. I liked the appearance, reliability & balance of this American too much to give up on it - there's a Shilen select match ratchet rifled 22RF blank in the lathe right now that will be turned down to the point where it won't take much bbl channel enlargement to make it fit. Hopefully, it'll shoot nearly as well as my little lightweight ACE 18" Ranch bbl on my V-22 carbine when I'm finished with it. It's probably a bit of a stretch to expect that much out of a mass produced, mid-range priced sporter, but chronographing decent ammo out of both these 457s gave comparable ES & SD numbers to what I was seeing out of the V-22s, and give how well the 457 MTR shoots, I felt it was worth the cost & work to re-barrel the American. Time will tell....