PB is a good powder for mid power loads. It is very bulky (like popcorn) so fills the case well. Try 3.8 to 4.6 gr
700X is an excellent, clean powder for mid power accurate loads. Try 3.7 to 4.2gr
Don't know C-300
I have used 700X with Lee 124gr TL bullets. I find it's a soft recoiling powder. I have used as low as 3.4gr with no issues. But any where from that up to 4.1 is decent.
As mentioned it appears to be fairly clean.
If you want a real smoke show. Tightgroup and a heavy Lee lubed bullet.




























