Daryl, Ducmarc, and others,
I am currently working on a 45-120 conversion double rifle using the 3 1/4 inch cases and some 350 grain hard cast bullets. I have proofed the gun using heavier 500 grain bullets and am in the regulating stage now. The gun is being built on a 12 gauge BRNO sidelock action and I have not been bothered by too much recoil. It is a joy to shoot even with just a plastic butt plate on it. By the time I am done with it, it will be restocked and fitted with a proper red rubber recoil pad.
I have looked at the 3 1/4 inch nitro express cases and found very little difference between them and the 45-120 cases. The 45-120 brass cases are from RWS I believe and measure a full 3 1/4 inches long. I also have some 45 basic cases from RCBS that were made in Sweden and I guess they were made by Norma. They only measure a little over 3 1/8 inches long. I have not tried loading any of them yet but I don't think the pressure will be affected much using the same loads, do you? I will only have to adjust the bullet seating and crimping on the shorter cases.
I don't ever foresee having to use any 500 to 550 grain bullets in this gun but the proof loads I used in it were heavy enough that if that ever occurs, the gun will hold the pressure produced. The gun will usually be shot using 350 and 400 grain bullets. According to Ellis' book, the conversions should hold up against 44,000 pounds but I don't ever consider that we will have to load it up to that pressure limit. It will be used mostly against wild hogs with maybe an occasional water buffalo thrown in. I am convinced it will do the job on both of those.
As to the Sharps company never making a 3 1/4 inch case gun, I have seen it in print both ways.
Some claim they never did, but others say a few were made very late in their production. Whether they did or not is really immaterial to me. If they did, they were too late to get much use in the shooting fields on American Bison. I won't be shooting one of those either. As far as pressure limits are concerned, in the proper gun, there is no reason to suspect that the .45-120 3 1/4 cases cannot be loaded up to .450 nitro levels as they are nearly identical. This is presuming that the new cases are of very high quality, of course. Bob