I have loaded all kinds of 223 rounds on my RL550. I just loaded some 77 nosler custom comps with IMR8208 XBR they all measured within 1/10 grain above or below. My gun never knew the difference. All the smaller grained powders work well. The one powder I know the dillon does not like for sure that you may use is varget. I throws off 2 to 3 tenths off allot. Matt