21.5 grains of IMR4198 and anybody's 50 or 55 grain bullet has been a very accurate load in every .223 I've owned* going back some 35 years, that covers at least eight of them and I might be forgetting one or two. It's also very good in a .221 Fireball. I'm sure more modern powders will outpace it for speed and temperature stability and all that but it's still just as accurate as it ever was.
It also works well in the .30-30 for cast bullets or reduced jacketed loads, around 19 grains was my best cast bullet load IIRC.
*except for a Mini-14 from the early 80's, that wouldn't shoot anything worth a damn.
