My Krag doesn't really like 30-30 bullets as well as the heavier ones. They may group OK, but it seems like they have to be loaded into the magazine more carefully than the longer ones. Only time I can recall getting "rimlock" was with 165 gr flat points.
I have been told Turner Saddelry makes really good slings, but doesn't always have them available for Krags, because of the length of the leather needed to make them. I have one from S&S, not the greatest.....made of two pieces, sewed together, and the joint falls right at the swivel when properly adjusted for me. Also, some of the holes are unevenly spaced.