WABI: That's been my experience with the Mustang also - it likes stiff loads. See my comment to your post "Can't get the Mustang to Group".

Also agree regarding loose bore on the Mustang. No bullet or bullet/sabot combo I've tried is difficult to load.

Glad you're getting her shooting. I'm getting there, but it's been in the mid90's here with 78+% humidity. Just too dang uncomfortable to play around on the bench.