It is best to use a powder that pretty much fills up the case. I believe the powders you listed, 4350 and RL 19, are both going to do that in the 243 case. They should both be quite good for your application. RL 19 and 4350 are also both quite good in the 270, and the 30/'06 as well. These two are so close together, one is not significantly better than the other.
Last edited by eldeguello; 07-24-2009 at 06:32 AM.