I've always thought that the 1:10" twist was "the right" twist rate for a 308Win. I'm looking at buying a CZ 550FS and they've got a 1:12" twist rate. Will this limit me to 150gr bullets?

My preference for the 308 is the 165gr pills.

If the 1:12" rate is too slow for 180gr bullets I won't care.

The 1:12" twist rate is standard for 308. It will stabilize 165/168 gr. bullets.
.

I too prefer a 1-10" twist for the 308.

However I have shot many 308's with 1-12" twist and they shot great with 180gr bullets.

In a couple of rifles they even shot the Sierra 190 gr. Match Kings.

On a hunting rifle, there is no problem with a 1-12" twist.

Some years ago while active in Long Range matches, Palma Matches, my Palma gun was a Rem. 40x w/ Krieger 30" barrel and 12 twist. It shot everything from 155's to 190's/Sierra of course/ very well. Those days with light winds to worry about, used the 155's, moderate wind used the 175's and on those nasty days at Perry or Oak Ridge, switched to the 190's. I shot it enough to know the performance of each load and could adjust the sight to fit the load. Don't think you can go wrong with the 12 twist and somewhere many years ago when the 7.62 Nato was being developed 10 was the original twist and later found the 12 worked better for them. The preferred twist for the 150 weight bullets is I believe a twist of 13, but you lose a lot of the versatility the 12 twist provides. Just my experience, but I wore out a few barrels with that twist and shot some decent scores as well. Good luck.

Mostly depends on bullet length with velocity also a being factor. I don't think any normal 165 grain length bullets will be a problem in a 308 Win with 1 in 12 twist.

But...FWIW some bullets types are very long for their weight class. This class could possibly be the only problem area I could think of. Unleaded bullets such as Barnes TSX, Tip TSX would be in this class of long bullets. Bullets with VLD type technology such as Swift Scirocco can also be very long for there weight class.

Examples of .308 bullet lengths are

180 grain Sierra MK ........1.280 length
180 grain Swift Scirocco II 1.440
180 grain Nosler E tip .....1.470
180 grain Nosler Accubond ..1.390
168 grain Barnes Tipped TSX 1.413

Own a Remington 700 308 Win heavy barrel with a 1 in 12 twist it shoots near bug hole groups with 180 grain Sierra Match bullets.

My 20" steyr shoots 180 SST's very well and its a 1-12".