SteveB, the conversion cylinder made by R&D is a drop-in. The 45 Colt conversion cylinder is made of 4140 and/or 4150 steel, it is safe, repeat, safe with smokeless loads. It is not safe for 45 Colt reloads noted for use in Rugers and Thompson Contenders. It is safe using "Cowboy" loads, see Hogdon's reloading info. I have shot thousands of rounds from R&D cylinders in 38 Special in converted Navies, and have shot many 45 Colt and Schofield in my drop-in 1860, both smokeless and black.
In a conversion it is the cylinder that takes the pressure, the barrel and receiver are not required to be of as high a grade of steel. One caveat is to buy some spare wedges from VTIgunparts, as the heavier, harder bullet hitting the forcing cone will be harder on the wedge of an open top gun. I use 200 gr, rather than 250 grain bullets in order to reduce the hammering on the barrel throat as well as to better match the slow round-ball type rifling.
The original percussion cylinder is not safe with anything but black powder or a sub. Even though 777 is a hot powder, and you will know you pulled the trigger, it is safe, pressure wise. NEVER load the cap & ball cylinder with anything but black powder or a bp sub.
hrminer92, my opinion of the Italian repros is that the Uberti is a better gun out of the box, but the newest Pietta Remingtons are almost too close to call as to comparative quality. That being said, Uberti is now offering a forged frame Remington that should be better than anything either company has made up 'til now.
I prefer the Uberti in the Colt repro beacause it is more authentic in shape, for some reason, Pietta has an odd rake to the backstrap that looks and feels wrong on both their Navies and Armies. In fact a Pietta 1860 will not even fit in an Uberti box.