I use fffg. If I fire with the muzzle over a clean, hard surface there is almost no unburnt powder residue, so it seems to be burning well. I was told to always use ffg, but for my rifle that was not the best. This rifle has been in constant use since I built it in 1981, was proofed with fffg when I made the breech plug and cut the threads for it. I don't expect it would burn 150 grains either, but where did that number come from anyway?
I wish I had access to a chronograph, which is the sure best way. Only way I ever had was fire over something and look for unburnt ejecta, and fire in dark and look for excess sparks in flame. My velocity figure came from a chart, so it is approximate. I get good penetration and expansion and great knockdown.
I was really just teasing some of you about modern stuff, and am sorry if I came off as being mean spirited or something. I have no problem with sabot loads and short fast twist barrels. I am just stuck in 19th century and like it there.
I just finished restoring a "Poor Boy" with a 44 inch barrel, not as a shooter, unfortunately, the bore was heavily pitted. I didn't weigh a charge from the old measure with it, but it impressed me as holding a heavy charge for the .43 bore. I did measure the pitch at one in 66 inches. I expect 44 inches of bore would burn powder O.K.
Target load for my .45 is 50 grains fffg. for best accuracy with RB, but this is not hot enough for clean kills on deer.
:-D