Well, I was going to start a new thread, but since this one was so handy

I will add my comments here for the 527 Carbine in 223 Rem. Yupper, I was offered a very reasonable price on a new 527 Carbine (and I had some gift cards) so I added a 4th 527 to my collection. All are good shooters out of the box IMHO.
I attempted some range time today, but it turned out very nasty

cold & windy, however did get my latest 527 acquisitions sighted in (a American 221 Fireball & the Carbine 223 Rem). The Carbine is a 1:9" twist & I love the feel & balance, initially mounted a Vortex Diamondback 4-12x40.
I experienced results similar to yours just testing a few on-hand, factory rounds; the Carbine liked Fiocchi 40 gr. VMax & 50 gr. BT, Nosler Varmageddon 55 gr BT, but it did not like the Federal 55 gr. V-Shock or Black Hills 77 gr Match Moly. I also tried a few rounds of Hornady 68 gr Match which were in between the good & the bad.
Range conditions being a big factor

I still feel this will easly be a sub-MOA rifle when I narrow down the ammo. I plan to use this rifle for hunting, so am hoping for a good 55 grain load as I have the 32, 40, & 50 gr covered with other 527's.
The 527 American 221 Fireball also did well - only had Nosler Varmageddon 40 gr. rounds for that but was very pleased with the results. I feel it will be a sub-MOA rifle as well.

those 527's.