I have the Kirst Conversion for the ROA. It seems really well made. The fit into the ROA was very nice right out of the box. I also have one for my Uberti BP for shooting 45 colt cartridge as well.
I don't know how to rate toughness. None are made to shoot over Tier One 14000 psi.
This is from Howell advertisement
" It will convert your blackpowder revolver to fire "Cowboy" ammunition. Only top grade certified steel (4150 Steel Cylinder and 4140 Steel Top Plate) is used in the production of these cylinders to offer superior quality, strength and safety. Due to manufacturing variations in revolvers, some minor fitting may be required.
Note: This conversion cylinder is for BLACK POWDER cartridges or black powder equivalent cartridges (also called Cowboy Ammunition) with lead bullets on a steel frame revolver ONLY. Attempting to use modern ammunition and/or installation on a brass frame will create a dangerous condition that can result in injury or death. "
and now a second type :
"This is the R&D Cartridge Conversion cylinder with loading gate for the .36 caliber Uberti 1851 or 1861 Navy percussion revolver with .375" grooves. You will need to drill and tap two 6-32 screws and cut the loading groove, complete instructions are enclosed. This cylinder converts it to shoot 38 Long Colt cartridge loaded with hollow base or heeled bullets. You can also use 38 Special hollow based wadcutter ammuntion. The cylinders are rated "For Black Powder or Equivalent Loads Only", which includes the current Cowboy Loads on the market. To overcome the larger bore of the original barrel, it is recommended that you use either hollow based bullets or heeled type bullets in your cowboy loads."
This R and D is nice having the loading gate, but in 38 colt. Howell has one as well. You don't have to pull the cylinder to reload. PITA
The conversion cylinder manufacturers ($275) seem to all say cowboy load only. The ROA toughness is not the question, it's the conversion cylinder that will blow first.
Buy a cheap used BH ($400) and shoot what you like. After buying two, I think conversion cylinders are NOT value purchases. I would rather have a second, strong sixgun than a PITA.
Prescut