Black Powder Test with 1847 Colt Walker

I used a Uberti copy of the 1847 Colt Walker to test my Corned Black Powder.
After the puck had dried for nearly a week in a window that got plenty of afternoon sun, I broke it up into smaller chunks and ran it through an antique coffee mill. The grind looked pretty course so I passed all but 40 gr through the mill again. It still didn't appear to be as fine as GOEX fffg,
With40gr in each load, I fired the GOEX fffg the 1st round. The 2nd round was my coarse grind, the 3rd round was a finer grind but not as fine as the fffg. The 4th round was GOEX again just for reference.
I believe that you can see my coarse grind was the best in the Walker, I'll have to run the same test in an 1851 Navy and an 1858 Remington to see if my course grind is still best for the smaller, lighter loads.
Note muzzle flash difference between rounds 1,4 with commercial powder and rounds 2,3 with my grinds. My powder is definitely burning too slow.