Mike-Actually, there were five 40 caliber chamberings in Sharps rifles. There was the 40-50 straight, 1 7/8" long; the 40-50 bottleneck, 1 11/16" long; 40-70 bottleneck, 2.25" long; 40-70 straight, 2.5" long, and 40-90 bottleneck, 2 5/8" long. So it could be any of them. All of the bottleneck 40's would have a rim diameter like a 45-70, the straights are smaller in rim diameter.