I disagree.
You really need to talk to the cylinder manufacturer.
R&D recommends..
"These cartridge converters are designed to convert your reproduction percussion revolvers to fire
Black Powder Cartridge & Cowboy ammunition"
"Attention!
This conversion cylinder is for
BLACK POWDER cartridges or black powder equivalent cartridges (also called Cowboy Ammunition) on a steel frame ONLY. Attempting to use modern ammunition will create a dangerous condition that can result in injury or death."
From Kirst.
"All Kirst Cartridge Konverters™ are precision CNC machined in the USA from 4140 Steel and heat-treated. The cartridge conversions are rated
"For Black Powder or equivalent loads only," which includes the current Cowboy Loads on the market."
A conversion cylinder in a open top may cause frame cracking at the trigger and bolt screw holes. This was a problem with the originals using black powder only.
Pushing a 250/255gr at about 900/1000 fps is a pretty stout load. I would not do it in a conversion cylinder.