Hello,
I also have a CZ 527 M1 American with synthetic stock, it was purchased in mid 2014. Actually the factory 3-shot target that came with the rifle is dated november 26, 2013.
I thougt It had a 1:9 twist, because the CZ webpage says it has, but CZ apparently changed the twist rate from 1:12 to 1:9 in early 2014. I measured the twist rate on my CZ 527 using the cleaning rod and it is unfortunately a 1:12 twist......
I have problems with most bullets heavier than 55 grains, the exception is the Federal Fusion 62 grains cartridge, it groups around 1" at 100 yards. Not sure why this bullet work, it must be something in that construction that makes it work in a 1:12 gun.
The Winchester 64 grains Power Max on the other hand did not work at all in the CZ 527 with 1:12 twist, the bullets was all over the place at 100 yards with 10-12" spread. Terrible!
Same story with the Barnes 55 grains TTSX copper bullet, I could hardly hit a 2x2 feet target at 100 yards. The Barnes TTSX bullet is too long (much longer than a 55 grains copper/lead bullet) so it will not work in a 1:12 rifle.
I have now tried the 50 grains Barnes TTSX, and it seems to work OK, but I am not completely satisfied with accuracy, it groups around 1.5" at 100 yards, not that great. I have reloaded with 24 grains of Norma 201 powder, using Norma cases. C.O.L is 55.6mm (2.189"). I measured the max C.O.L to 56.6mm (2.228") with the 50 grains TTSX bullet, so i have 1mm of headspace.
The Norma case by the way has more volume than the S&B cases (and most other 223 cases), so I have to use 1 grains less powder in S&B cases.
I will now try 25.5 grains of Vihtavuori N-140, to see if a bit slower powder will work better. I tried the 55 grains TTSX with 25 grains of Vihtavuori N-140 and it cronographed at 2870 f/sec. So I assume 0.5 grains more powder with a 5 grains lighter bullet will be OK.
The S&B 55grains FMJ bulk ammo works OK, but accuracy is not that great (1.5"+ at 100 yards). The best factory ammo I have tried so far is the RWS 55grains SP and the Norma 53 grains SP, but the CZ is a "touchy" gun when it comes to ammo.
I just wish I had the 1:9 twist version......
I think I will replace it with a Howa Mini Action or a Sauer 100 Classic XT 223rem when I can afford it.
Best regards
223 gunner from Norway