I can relate to wondering how many groups they shot at the factory before they got one good enough to meet their standards. My very first CZ 22RF was a 457 American purchased Jan, 2019. The test target didn't look all that bad, but when I started shooting it at 50yds, I couldn't get anything close to it. I had several lots of SK Std+, a very good lot of SK Rifle Match, and a few lots of older Lapua - none of it would do better than 1.5" at 50yds, even after I'd worked to get the trigger down to just over 1lb. and re-cut a precision 11* crown to clean up the ragged mess of a factory crown. I'd put around 500rds through it with no notable improvement in accuracy when I gave up on the factory bbl. It was too nice a rifle to dump, with extremely smooth & reliable function, and I really liked the appearance/proportions - and besides, I wasn't going to sell a rifle with accuracy that poor to anyone else. I got a Shilen ratchet blank in #5 contour, cut off the 1.2" dia shank, and then did some minor contour work, cut a fairly snug tenon, chambered it with an EPS reamer, cut the extractor slots, shot it with a mix of CeraKote tungsten/graphite black, and glued it into the action with Loctite #609. I feel it was worth the expense & effort, as I've now got what I consider to be a good looking rifle that shoots at least as good as it looks.
Had a similar experience when I bought a 457 VPT with a Manners PRS1T stock: was trying to get the bore clean before taking it out to shoot with it, and just kept getting black gunk out of it. Checked the bore with a Hawkeye borescope, and found an area about an inch ahead of the chamber, about 1-1/2" long, that was covered with what looked like spatters of melted lead covering the bore. I went after it with a bronze bore brush, and easily removed it, but had to wonder how many rounds they'd fired at the factory to get that much lead fouling. It never reappeared during the process of putting several hundred rounds through the rifle, so it's a mystery to me what caused it in the first place. I thought this rifle's 50yd accuracy improved a bit as I put several hundred rounds through it, but when I backed-off to shoot 100-200yds with it, the groups just fell apart, and I wound up putting another Shilen ratchet on it, going with a .860" straight blank, and finishing it at 22".
The only 457 I've bought that shot good enough from the factory to leave the OEM bbl on it was a Varmint MTR, with what they call a 'match' chamber. It's respectable in the accuracy dept, but since I've got the Shilen barreled American & VPT, I really have no use for the MTR.