Howdy
Taylors and Howell are two separate outfits.
Years ago when I bought the conversion cylinder for my 1858 Remington, Taylors was marketing cylinders made by Howell under the R&D name. When making a 45 Colt conversion cylinder for the 1858 Remington, Howell discovered the basic cylinder is too small to have six 45 Colt chambers because the rims of the cartridges would overlap. So he bored his chambers at a very slight angle so the rear of the chambers had a little bit more space and the cylinder could accept six 45 Colt chambers without the rims over lapping. Howell obtained a patent on his design. Before anybody gets their undies in a twist, the angle is very, very slight, less than 1 degree, and does not affect the accuracy of the revolver at all.
At one point, for some reason Howell sold the rights to his patent to Taylors. Taylors then had the cylinders manufactured by another outfit, but they were the same as when Howell was making them.
A while later Howell set up his own company to make conversion cylinders, but he was prevented from making the six shot 45 Colt cylinder with angled chambers because he had sold his patent to Taylors. That's what can happen if you sell the rights to a patent.
So for a long time the only 45 Colt conversion cylinders that Howell offered for the 1858 Remington were restricted to five chambers. Don't be confused by the
44 Colt cylinder he offers that has six chambers. That is for a smaller cartridge and 45 Colt will not chamber in that cylinder.
Most recently I heard that Howell's patent has run out, and he is again offering a six shot 45 Colt cylinder for the 1858 Remington. If you go to his website you can see it.
Anyway, that is the story with Taylors and Howell and six shot 45 Colt cylinders for the 1858 Remington.
https://www.howellarms.com/