Yes they will stabilize just fine with a 1/12 twist. I’ve had 3 different rifles in .204 Ruger, a Thompson Contender, a Ruger Hawkeye and a CZ 527 and all were 12 twists and I’ve shot ALOT of Hornady 45 grain softpoints they are accurate and do a real good job on Coyotes both killing them and not blowing them up. RL15 has worked great for me and if I remember off the top of my head it was like 26.3 grains