The chambers of the 6 shot were offset by 2 degrees which allowed them to fit in the cylinder, but weren't as perfectly aligned as the 5 shot chambers.
Folks didn't complain about their accuracy and many more probably wish that they could still buy them.
That is incorrect.
The chambers on the original R&D 45 Colt six shot cylinders for the 1858 Remington are angled at less than 1/2 of one degree.
Originally designed and manufactured by Ken Howell under the R&D brand. Howell patented the angled chamber design. Taylors was the exclusive distributor. At some point Howell sold his patent to Taylors, who contracted with another manufacturer to manufacture them. Thus, Howell was prevented from making a six shot 45 Colt cylinder for the 1858 Remington because he had sold the rights to his patent. A six shot 45 Colt cylinder with angled chambers is still available from Taylors.
I bought a R&D six shot 45 Colt cylinder for my EuroArms Remmie many years ago.
I actually prefer shooting 45 Schofield in my Remmie has opposed to 45 Colt. This is because I actually shoot mine with cartridges loaded with Black Powder. I don't think I have ever fired Smokeless cartridges in mine. Loaded with Black Powder, the Schofield case has less powder capacity than the 45 Colt case, and I use a 200 grain bullet, rather than the 250 grain bullet I use in my 45 Colt Black Powder loads. This makes for less recoil, because of the lighter bullet and lower powder charge.
The other reason I prefer the lighter loads is because the frame is very thin where the loading lever pierces it, and I always worried about what the pounding of recoil with the heavier loads might do to that section of the frame. Even a Black Powder 45 Schofield develops more recoil than the typical percussion load under a .451 round ball.
In fact, I designed the first 200 grain Big Lube bullet for 45 Colt when the only other bullet available was the 250 grain PRS Big Lube. I did this to have a 200 grain Big Lube bullet that could be loaded into my Schofield cases.
This photo shows five different 45 caliber cartridges. Left to right they are 45 Colt, 45 Schofield, 45 Cowboy Special, 45 Auto Rim, and 45 ACP. The 45 Colt is one of my Black Powder rounds with the 250 grain bullet, the Schofield round is one of my BP rounds with the 200 grain bullet.
I actually have two Remmies with the R&D cylinders, a bunch of years ago I found a used Stainless Uberti Remmie at a gun show that included a Conversion cylinder.
The 1858 Remington is the only Cap & Ball revolver I ever considered buying conversion cylinders for. Unlike a Colt, where you have to pull the barrel off to reload, unless you carve a reloading groove or fit a loading gate, the Remington is simple to reload. You drop the loading lever, pull the cylinder pin forward, and pop out the cylinder. The cap is a loose fit and comes right off to reload. I pop out the empties, reload fresh cartridges, then pop the cylinder back in place.
It is as quick and simple as Clint Eastwood makes it look in Pale Rider. (note: commercial conversion cylinders were not available when that movie was made, the cylinders were made up by the prop guys. Bit it is as quick and simple as Clint makes it look.)
Historically there were many different designs for conversion cylinders to convert percussion revolvers to shoot cartridges. I am not going to go into all of them here, but you can read my comments about the subject here:
https://thefiringline.com/forums/showthread.php?t=608787
Historical note: The six shot R&D cylinder with its separate cap is not a historically accurate replica of a conversion cylinder. None of the old designs used a removable cap with separate firing pins. I like the R&D version for the reasons I stated above. Quick and easy to reload. As I said, I only shoot mine with Black Powder. I began shooting Cap & Ball revolvers in 1968, and in my experience a cartridge conversion is quicker to reload and shoot, and no worries about pieces of broken caps falling into the mechanism. That's why they were developed during the Civil War.
About the cost: Yes, they are expensive. Just under $200 when I first bought them, about $240 these days. My rational was I bought my EuroArms Remmie back in 1975. I have no idea what I paid for it, but after over 20 years the actual value was next to nothing, so spending about $190 on the cylinder was like buying a new gun for $190. The used Stainless Uberti that came with the R&D cylinder was a bargain too, otherwise I would not have bought it.
One more comment: Those of you with experience with the Remington 1858 know they foul very quickly. That is because there is no collet on the front of the cylinder to divert BP fouling blasted out of the barrel/cylinder gap away from the cylinder pin. The pin is very narrow, only about 1/4" in diameter, and fouling blasted onto it builds up quickly, working its way between the pin and the cylinder, causing the cylinder to bind very quickly, after only a few cylinders full. Colt Cap & Ball revolvers had an arbor much wider than the Remington cylinder pin, and Colt cut a helical groove onto the arbor to provide clearance for fouling to build up without binding the cylinder. The Colt replica shown here is a Pietta replica of the 1860 Colt Army. You can see I cut some grooves into this Remmie's pin to hold some bore butter to help keep the cylinder rolling, but that never helped much. I find that with the Remington 1858, every time I pop the cylinder out to reload I wipe off the face of the cylinder with a damp towel to keep the fouling to a minimum. That way I am able to shoot a lot more than just a few cylinders full. By the way, the two bullets shown at the bottom of this photo are the Big Lube 250 grain PRS bullet, and below it my 200 grain J/P 45 200 grain Big Lube bullet. The huge lube grooves are what makes these bullets work so well in Black Powder cartridges. I receive no money for my design, I did it to fill a need. Molds for these bullets are available at the Big Lube website.
https://www.biglube.com/
I have both versions, 45C and 45ACP for the ROA’s and Rogers and Spencer, all 6 shot. A five shot for the Colt 1860 Army. Looking at Taylor’s conversion for my Remington Revolving Carbine which is the same for the Uberti Remington NMA. Photo is a couple years back. Two ROA’s 45C and 45ACP and a Uberti 1860 Army. 
