I got out to shoot my 12.7 X 44 R rolling block sporter. 70 gr, FF under the 340 gr. 515139 Lyman. MV was 1300fps, factory equivalent. Loaded in .50-70 cases, shortened and with the rim trimmed a bit. Worked well for a 137 year old rifle and 64 year old eyes! 1 3/8" group @ 50x, but I had to raise the second leaf on the open sight.
I'll try it next time at 100x and 150x, and then go for moose, like my Dad in the old country.