Microgroove often likes oversize bullets. With hard bullets, you need to try some at .359. It may even like them as large as .360. If buying from a local caster, he may be able to accomodate. Check around, there may be a caster there in your town or Blanco or Llano that might run up a few for you to try in different sizes. If not, try giving Lone Star in Halletsville a call. Might get 100 apiece in .358, .359 and .360 and see which is best. His are plenty hard. Wouldn't cost that much to try. The diameter and hardness have more influence on a Microgroove than powder. Your 2400 will be just fine.