The Steel Framed Models can be converted to a centerfire cylinder can't they & I don't want that The Pietta 1858 12" is the model I am getting buy now I am very concerned that I will wear it out shooting it I am gonna see if I can find a Steel Frame Pietta 1858 Bison/Buffalo 12" I can use a shoulder holster
Just because conversion cylinders are available does not mean you must obtain one.
Any brass frame will "Shoot of time" eventually. Sooner, rather than later, if you use loads that lean to the "heavy" side. (over 20-25 grains. Be aware that you may need to use a "heavier" charge to seat the ball fully on the powder. As with a rifle, you do not want a gap/air space between the powder and ball.
One of my revolvers had a "Short Stroke", I'd guess, when pressing the ball into the chamber using the "recommended" powder charge. I had to up it by 5 grains to get the ball seated on the powder. (Over powder wads for revolver had not been invented yet when I had that one.)
Truth to tell, I never thought of putting 5 grains (compressed volume) or so Cream of Wheat between the powder and ball. I always put it on top of the ball to seal the chambers. Adding 5 grains of powder and putting the Cream of Wheat on top was easier/less hassle and possibly a little faster.
Only time I put the Cream of Wheat directly on top of the powder was if I was shooting blanks at a CW reenactment.
(25 grains FFFg or P grade Pyrodex, Cream of Wheat compressed flush with the chamber mouth. was my blanks load.)
BYW: If you do decide to get a conversion cylinder, you do not have to modify or replace the hammer to fire the
black powder loaded "Cowboy Action" cartridges. The cylinder "end cap" has six firingpins that are hit by the standard C&B hammer.
Cartridge or not, you still don't want smokeless powder anywhere near your revolver.
Why are you set on a 12 inch barrel, if you don't mind my asking?
Bat Masterson never had one, no matter what dime novels, urban legend, and Hollywood claim.
Because of the barrel and chamber gap, a longer barrel will not add to the velocity.
A 12 inch barrel will just make carrying more difficult and the revolver clumsy, since the balance will be off..