Took the Lyman Mustang to the range this afternoon and found out a few things.
#1 - it groups better since I removed the scope
#2 - it likes Barnes 250 grain Expanders
#3 - it shoots way high with 250 grain shockwaves (about 4" high @ 50 yards, while the Barnes 250 grain expanders were right on at 50 yards)
#4 - it likes Jim Shockey gold without swabbing between shots ????
tried 3 shots at 50 yards with a dirty barrel and grouped less than 1" - swabbed the barrel and the next shot went 2" high.
I was shooting 120 grains fffg Jim Shockey Gold for all the bullets & weights today.
#5 - it's too hot to do any serious shooting
I'm going to wait until it cools off some before I do any really serious furthertesting of this combination. Just too hot for the barrel to cool down like it should (and I was dripping sweat, too).
I'm starting to think the Mustang might have a slightly oversize bore. The Barnes bullets are normally very tight to shove downbore in most of my rifles, but they go down with relative ease in the Mustang. Not drop-in, by any means, but just moderate pressure on the ramrod slides them smoothly down the bore.

It would sound to me like you had a good range day and learned a great deal about your rifle. Its the only way I know of to figure them out. Range time is the one thing that makes these rifle shoot better.... It was to hot and humid here today also to shoot. I had everything ready to go outside and then it rained for 10 minutes. After that the real sauna started.

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.