I know a lot of people use 777 and a lot of people complain about the crud ring. My recommendation would be to try some Swiss either in 2F or 3F if you can find it. From what I hear and from what I've been told by the owner at Dixon's ML store here in Hamburg PA. It's the best powder on the market for ML's. Plus you will find that it is only a couple dollars more expensive than 777. Don't know why 777 got to be so expensive.

Anyway just my 2 cents.