I have a Sig 556 with a 1:7 twist rate which loves the heavier bullets like 60+. I am buying a Remington 700SF heavy barrel with a 1:12 twist to use as a dedicated prairie dog gun along with my two 17HMR's. I assume with that twist rate it will like the lighter bullets like 40, 45, and 50 and possibly 55gr. Any thoughts? I know the Sig will handle all the way down to 55gr if I use FMJ, but the VMax loads don't do well in that rifle. Thanks in advance.

According to Shilen's website a 12 twist is good for bullets up to 63 gr. Berger says a 12 is good for their 60 - 64 gr bullets (.224) Looks like that 7 twist is good for 90 gr bullets.

You might want to read this for reference -
Greenhill Formula

my cz 527, and rem 700 1-12 twist like the 50gr v-max and 25gr h-322. this was close to max load and the rem liked them, so i used same one in the cz and it likes the load too. used same one in my dads cz with good results also. i do not have a lot of time to experiment with loads.

Good to hear about the 50gr V-Max. I was considering that one as a good possibility. Fiocchi makes some and the price is pretty decent right now too. Thanks.

although the 12 twist 223 is supposed to be good for up to 60+ grain bullets, I've had some that didn't shoot anything over 50-52 grains real well. The 50 grain bullets are a pretty safe bet, but it still may prefer one bullet design over another. e.g. mine shoots Hornady 50g SPSX better than 50g Sierra Blitz Kings.