Howdy
I designed machined parts as a mechanical designer for a good many years. Perhaps I can speak to this question with a little bit of authority.
When specifying machined parts, unless there is a specific reason to maintain a sharp edge, it is standard practice to specify a chamfer to break the edge. A chamfer is a flat surface connecting two other surfaces. This is done for several reasons. Primarily it is done to prevent injury to anyone who handles the parts. It is also called out because once parts have had a finish applied to them, like blueing in the case of a firearm, a sharp edge that has been bunged up will stand out like a sore thumb, whereas the finish will not be quite as easily damaged on the broader chamfered surface.
A chamfer will usually be relatively small, so as not to remove enough material to significantly weaken the part. Chamfers are usually called out as 45 degrees, unless a different angle is required. On turned parts such as a revolver cylinder, a chamfer is either made by feeding a cutting tool set at an angle into the edge of the part while the part is turning, or by feeding a cutting tool into the edge at the specified angle. This is a simple operation on a conventional lathe.
I don't own a Super Blackhawk, but here is a photo of a couple of replica Cap & Ball cylinders. The cylinder on the left is from a recent Pietta replica of the Colt 1860 Army and the cylinder on the right is from an old EuroArms 1858 Remington Replica. These chamfers are about .02 X 45 degrees. Both are relatively poorly done, exhibiting chatter marks. I also have a Stainless Uberti 1858 Cylinder, and it exhibits almost no chamfer at all.
In the 19th Century, standard machining practice would have been to cut the chamfer on a lathe as a final cut after many of the other major machining processes had been completed. Modern CNC tool centers can cut a chamfer like this as part of the machining program and would not require removing the part from the toolholder. Since my 1858 Uberti cylinder is relatively new, I suspect a tiny rounding over cut was made while the part was still on the tool holder, resulting in a broken edge that is barely visible, but still does not cut anybody handling the part.
This next photo shows two Colt cylinders on either side of a New Vaquero cylinder.
The cylinder on the right has what is known as the Black Powder Bevel. Notice the depth of the chamfer varies. This was a complicated cut, not possible to produce on a standard lathe. The chamfer would either have to have been cut on a special fixture that rotated the chamfered face past a grinding surface or a cutting tool, or it would have had to have been done by a very skilled worker manipulating the part by hand past a grinding surface. I do not know which method was used, but it would have added significant expense to the part.
The cylinder on the left is a standard 2nd Generation Colt cylinder. It exhibits a simple 45 degree chamfer running around the front of the cylinder, interrupted by the flutes. This chamfer is about .03 X 45 degrees. I have shot this cylinder a great deal, and you can see the typical holster wear patterns that form on the outer edges of the contours from repeated drawing and reholstering the gun.
Lastly, the New Vaquero cylinder in the center exhibits what Ruger was calling their version of the Black Powder Bevel when they first brought out the model. It bears little resemblance to a true Black Powder Bevel, nothing more than an exaggerated rounding over of the front edge of the cylinder.
This last photo shows an 'original model' Vaquero at the top and an Uberti Cattleman at the bottom.
The Vaquero cylinder is treated about the same as a 2nd Gen Colt. A simple 45 degree chamfer interrupting the flutes. The Cattleman does indeed exhibit a true Black Powder Bevel. Since the it was produced on modern CNC equipment, the Black Powder Bevel was probably produced by the CNC programming while the part was still on the toolholder, not requiring the expensive extra operations of the original Colt Black Powder Bevel.
You will hear a lot of explanations for why the Black Powder bevel existed. Ruger claimed that their version made the gun easier to return to leather, since the New Vaquero was designed originally for the Cowboy Shooting market. Frankly, I don't buy it, I don't have any difficulty returning any revolver to leather, no matter what type of bevel it has.
As to why Colt is not supplying the Black Powder Bevel today, that is a good question. In the days before CNC equipment, the old Black Powder Bevel was clearly more expensive to produce. That is why the 2nd Gen Colts did away with it starting in 1956.
Just about all modern revolvers will have their cylinders made on modern CNC equipment. So any good CNC programmer should be able to program the Black Powder Bevel into their programs. It would require a complex multi axis machine, capable of holding the part stationary while a spindle moved around the part, cutting the profile. Another way of doing it would be as a separate operation on a CNC miller. USFA seems to be providing the Black Powder Bevel in many of their single action revolvers, but not all. As I mentioned earlier, Uberti is doing it too, at least with the one that I own.
Make no mistake, cutting extra features onto any part is going to be more expensive. Modern production costs are directly related to 'tool time'. The amount of time the cutter is actually removing metal. Cutting a Black Powder Bevel will mean more time needed to cut the more sophisticated shape. Less parts can be produced per day, and that means it costs more. But USFA and Uberti seem to be doing it. Clearly not a priority with Ruger.
Personally, I find the true Black Powder Bevel to be more aesthetically pleasing to look at. I'm sure that's why it was done in the old days, when skilled labor was relatively cheap.