A lot of thought went into configuring this rifle prior to ordering it two years ago. Of primary consideration was its intended use as a hunting rifle, of course. That drove both physical size and weight, determined through barrel length and contour along with stock configuration. The other primary consideration was, of course, a suitable hunting caliber.
Fortunately, I have a number of Sharps pattern rifles that are far too big and heavy, so I had ready examples of what I did not want. Additionally, however, I have an original Remington Hepburn of a configuration that carries and balances superbly. It served as the pattern for this rifle as far as barrel length and configuration. The only real deviation was where I chose to go with the more traditional straight grip stock for the Sharps:
I could not be happier in just how closely the Sharps mimics the handling characteristics of the old Hepburn. It came out exactly as I had hoped.
The other consideration was caliber. It was going to be a .45, the only question being that of case length. I firmly believe that the modern, solid head .45-70 case is under capacity as a hunting round when used with black powder. Great target round, but lacking punch for hunting. I've used the .45-2.6" (.45-100) in long range match shooting for over 20 years with great success, but have always found fouling control to be a challenge, even under the controlled conditions of a match.
The .45-2.4" (.45-90) neatly splits the two. Enough capacity to generate the punch required for our largest game, but not the copious fouling of the bigger dedicated match cartridges. Under field conditions, one can fire two or three accurate shots without having to stop and wipe the bore, which would be impossible with a larger case.
So .45-2.4" it was. Made even more attractive by the fact that the old Hepburn happened to be in the same chambering. I could even have ammunition commonality, always a good thing. Except, darn it, it didn't work out that way...
You see, 19th century cartridge rifles are notorious for big, sloppy chambers, and this Hepburn is no exception. Ammo fired in it comes out somewhat oversized. I'm loathe to full length size it, which only results in work hardening it and dramatically shortening the life of the brass. The Sharps has a modern, tight chamber. It will not chamber brass fired in the Hepburn unless it is full length sized.
To further complicate things, the front of the Hepburn chamber is undersized, and will not accept bullets over .457" diameter. The Sharps will accept bullets at .459" dia. Shooting undersized cast lead bullets generally results in poor accuracy and leading. In summary, cases big enough to suit the Hepburn won't chamber in the Sharps and bullets big enough to suit the Sharps won't chamber in the Hepburn. So they are, essentially, two different calibers requiring two different lots of brass and two different sizes of bullets. The best laid plans...
You can even see, visually, the bulge in the case that came out of the Hepburn (on the left). Not a big deal in the least, with black powder, if it keeps getting used in the same rifle and never gets sized. You'll get a hundred reloads out of it. Keep sizing it down so it looks like the one on the right, and it will split in less than ten:
How they don't fit in each other's rifles:
That's as far as they go into each other's chambers until the larger diameter bullet stops it in the Hepburn, and the case bulge stops it in the Sharps. The only "solution" would be the small bullet in the full length resized case, which would not be ideal in either. Thank God for hand loading, I guess. And retirement...