Since you're going to be loading .308 in the future and already have .223 there are a lot of powders that work between the two. IMR-4895, H-4895, Varget, N-140, RE-15 are probably the ones that will work the best overall. Unless you're wanting to smoke the smaller .22cal projectiles then H322, N130, N135, IMR-3031 work nicely in a 223.