I've got three CZ457s - American, Varmint MTR, and VPT. The factory barrel on the American was a stinker, never did get it to shoot much better than 1-1/2" groups at 50yds, even after pulling the bbl and cutting a nice clean 11* crown to clean up the fugly mess from the factory. The MTR shot pretty decently right out of the box - only things I did to it were to adjust the trigger & spin up a home-made bolt knob similar to the A419. The VPT was the 24" bbl version, and that bbl had issues out of the box, with a bunch of melted lead spatters covering a 1-1/2" long section of the bore about an inch in front of the chamber - and this was before I ever fired the rifle. A cleaning session with 10 back-and-forth passes with a bronze bore brush saturated with Shooters Choice got rid of all but a tiny bit of the lead spatters, and accuracy improved a bit. But after putting 400+rds through it - with periodic cleaning - I decided to back off to 100-200yds to see what it'd do, and found that I couldn't keep 10rds of good lot-tested SK Rifle Match on an 8" steel plate at 200, on a day with good conditions.
I should mention that I'm used to much better accuracy out of my 22RF bolt repeaters, including a jelrod-converted CMP 40XB with a Krieger bbl that I fitted & chambered, as well as a couple of V-22 repeaters with Kriegers that I also chambered with a PTG EPS reamer. I liked (and still like) the 457 actions, so I pulled the factory bbls off the American & VPT, then replaced them with Shilen ratchet blanks that I fitted & chambered - again with the same EPS reamer, without cutting the big grub screw seats, instead gluing them into the actions with a fresh lot of Loctite #609. So, in my admittedly limited experience with CZ's OEM hammer forged barrels, 2 out of 3 were problematic where accuracy's concerned, and those two rifles shot much better with the glued-in Shilens. However, I've read a lot of posts here & on other sites where owners of the heavier barreled 457s seldom seem to have accuracy issues like mine. No way of knowing with any certainty if that's actually a trend, but it's food for thought.