I couldn't find any Trailboss for my Krag at the gunshow Saturday but got talked into a can of Tin Star. I wasn't really impressed with TB as I went through a can in no time. I am very impressed with Tin Star. The big group is 2 different style 170 gr lead gc bullets and 125 gr lead RN bullets. They seem to shoot in about the same spot. POI was 6 o'clock on the red dot. 40 yds with bags. I'll clean the bbl good tonight and load up some more. Try again tomorrow.

It's new to me too. According to this chart, Red Dot-Trailboss-Clay Dot then N320/ Tin Star, which is slightly different than N320. I don't know if the chart will work as a screen shot.

I hunted about on the net for info.  The stuff VERY FAST and is designed for Cowboy Action shooting; little fouling and no great demands for accuracy.  It is for use in straight cases (capacity less than 50 grains of BP)  with relatively lightweight (for bore size) lead alloy bullets.  That means pushing a 200 grain bullet at about 700 fps out of a revolver, with a big space for gas to escape.

The Krag case is bottlenecked, with just less than twice the case capacity.  Plus the Krag has a reduced bore.  With the 170 grain bullet, you are trying to push a slug with much higher density (weight/cross-sectional area of bore), so the cork is a lot harder to push out of the bottle.  I think you are risking your eyesight, your fingers and an old Krag.  It is a risk I would not take.

Guys have been reloading Krag cases with lead alloy bullets for 120 years.  There is not much in modern reloading manuals, but the old manuals have lots of info.  The best of the bunch is Phil Sharpe's "Complete Guide to Handloading", 1937, with a long-expired copyright.  It is available as a free download on the net if you search.

Beginning in the 1930s, most of the old-timers used IMR 4198 or IMR 3031.  Those powders are still on your burn chart. Check out the relative burn rates.

That said, I have a 32-20 Low Wall.  I think I will try Tin Star in it, pushing 3118.

Seems to me that your 9.7 grain load should be fine, fitting in with medium-burning powders cited by C.E.Harris for loads in this class -

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Very nice group!

I experimented with 3 different 170 gr bullets the other day out of my PC rifle. I had been using my NRA but I did the repair on the PC stock. Same 10.0 gr Tin Star, 40 yd off a bag. Two were .308 (lead and jacketed) and one was .310 ( lead gc). I got a 1 inch,  one hole group with the .310 and a 2 in+ with the.308. Guess I know what the PCs bbl likes. This week I'll shot the PC against the NRA? Carbine and see what I get.