Howdy
First off, you need to know there are three different outfits making 45 Colt conversion cylinders for the 1858 Remington, and they are all different.
There is the Kirst five shot version, the R&D six shot version, and the Howell Old West five shot version.
A little bit of history is involved here. It is physically impossible to bore six parallel 45 Colt chambers in a cylinder that will fit in the 1858 frame and not have the cartridge rims overlap. The distance from center of the cylinder to center of the bore simply will not allow it. So there have been three separate solutions to the problem. Kirst went with a five shot cylinder with a 'dummy' position. The five 'real' chambers are spaced so that rims will not overlap and the 'dummy' position takes up the sixth position. The ratchet teeth are arranged to allow for the different spacing. In addition, Kirst uses a spacer plate that is screwed into the frame with just one stationary firing pin. The beauty of the 1858 revolver is that it is quick and simple to pop the cylinder out for reloading, so if you want to pop the cylinder out every time you reload, that is not a problem. If you want to load through a loading gate, you must cut a groove into the frame where the loading position would be. There is no actual loading gate, the position of the cartridges when the gun is loaded keeps them from falling out. Just don't point it skyward when you cock the gun, or a round may try to fall out of the cylinder. Many of the original Remington conversions were done exactly this way.
http://www.kirstkonverter.com/shopdisplayproducts.asp?page=1
Kenny Howell had a different idea. He angled the chambers out ever so slightly, less than 1/2 of one degree, so that six 45 Colt chambers could be drilled and the rims would not overlap. Before you ask, no 1/2 of one degree makes absolutely no difference either safety wise or accuracy wise. The bullets make the transition from chamber to bore with no trouble at all. In addition, rather than using a spacer plate screwed to the frame, Kenny Howell used a separate cap for the cylinder that rotates with the cylinder. The cap has six separate firing pins, one for each chamber. With this design, you pop the cylinder out to reload, cutting a loading gate slot would not work. Again, since the cylinder pops out of the 1858 so easily, this is a very efficient system, pretty much the same as Clint Eastwood did it in Pale Rider. These cylinders were marketed under the name R&D and were marketed exclusively by Taylors. If you see them on sale from another distribution, they bought them from Taylors.
The idea for the angled chambers was different enough to be patented, and Kenny Howell patented his design. At some point, Taylors bought the patent from him. Taylors continues to sell these six shot, angled chambered cylinders, but they are manufactured by somebody other than Kenny Howell.
http://www.taylorsfirearms.com/conversion-cylinders-for-1858-remington-steel-frame-44-caliberbp.html
Lastly, fairly recently Kenny Howell himself decided to get back into the conversion cylinder business, but since he sold the patent for his six shot cylinders he can no longer produce them. So all the 45 Colt cylinders for the 1858 that Kenny Howell's Old West Conversions company sells are five shots, with a multiple firing pin cap similar to his old six shot design.
http://www.howelloldwestconversions.com/shop/productinfo.cfm?catID=261&productid=818&cfid=2974143&cftoken=634c1f4b02ec14b7-2491C470-923F-0C65-30A44DDD655DCBDD
When I looked into this a bunch of years ago I decided to go with the six shot version being sold by Taylors.
That is an old EuroArms Remmie that I bought in 1975, it turns out the cylinder for a Pietta fit it just fine. Yes, there are slightly different chamber spacings for the Pietta and Uberti versions. There was another one for the Ruger Old Army.
The chamber throats on this cylinder are right on the money at .452. The actual groove diameter of my old Remmie is .449, rather than .451, so I always shoot bullets sized to .452 in it. I always shoot it with Black Powder, either 45 Colt with about 35 grains of FFg and a 250 grain soft lead bullet, or 45 Schofield with about 28 grains of FFg and a 200 grain soft lead bullet. I usually use the Schofield load as it stresses the frame less at the very thin cross section where the loading lever passes through the frame. These cylinders are made of modern arsenal steel, and are stronger than the original C&B cylinders. It is specifically recommended to stay with 'cowboy loads' if you are going to shoot Smokeless in them. No hot stuff, and lead bullets only! As far as tolerances are concerned, I have two Remmies equipped with these cylinders, and they are the most accurate 45 Colt revolvers I own, more accurate than my real Colts, Rugers, or clones. This is because the tolerances on the chambers are very tight. I actually use one of these cylinders as a cartridge gauge when loading 45 Colt. If a round drops into them, I know it will drop into the more loosely toleranced chambers of a Colt, Ruger, or clone.
