I'm a greenhorn, but was looking at the same thing. I thought it would be great to have a converted army pistol, but in "my" caliber, .44. (I haven't bought a single gun yet, but am planning: .44 across the board in revolvers and rifles for Period Correctness and convenience).
Howdy
You are making this much more complicated than you have to.
A few definitions.
Bore: The diameter of a hole when it is drilled. Sometimes the verb bore is used instead of the verb drill when referring to making a hole.
Groove: The extra depth the 'bore' has been cut when rifling is created.
When a rifle barrel is made, first a hole is drilled (bored). Then a second tool is run through the bore to cut the rifling. There are several ways to do this, but the end result is a set of grooves running the length of the barrel in a helical (not spiral) pattern.
Once the rifling has been cut, the part of the original bored hole that remains is the lands. So with a rifled barrel you have grooves and lands. Peer down a rifled barrel some time with a strong light and you usually see tool marks running across the lands. These marks left behind by the spinning drill. They are all that is left of the original hole when it was bored. However the tool marks left in the grooves will be running the length of the barrel because the cutter that created the grooves was pulled through the barrel.
So when somebody uses the term 'bore' and 'rifling' interchangeably, they are actually incorrect. The bore is the inner diameter where the lands are. Groove Diameter, or Rifling Groove Diameter is the correct way to to refer to rifling diameter.
Heeled Bullet: Pull the bullet out of a 22 rimfire cartridge sometime with a pair of pliers. That is a heeled bullet. The bullet is the same diameter as the outside of the cartridge case. The 'heel' is the narrower section that slips inside the cartridge case.
At about the same time that revolvers were being transitioned from Cap & Ball to cartridges, cartridges themselves were still being developed. There were quite a few competing designs on the market. Things like rim fire, needle fire, teat fire, centerfire, and a few others. Cartridges had not been around for very long, and the market place had not yet weeded out the inferior designs. Heeled bullets were one of the designs that have since fallen by the wayside. rcflint is correct. The first cartridge conversion revolvers were made by sawing off the rear most portion of a conversion cylinder, where the nipples were. This left a straight hole through the cylinder, no step as in a modern chamber. So a cartridge having the bullet and brass case of the same diameter was going to work best in such a cylinder. And that is what was used in most of the early revolvers that were converted from Cap & Ball to cartridges during and shortly after the Civil War.
But the problem with heeled bullets was they carried their bullet lube on the outside of the bullet. That's why there is a waxy coating on modern 22 Rimfire ammunition. Bullet lube to keep the bullet lubricated as it slides down the barrel. But in Black Powder days bullet lube was soft and gooey. It would attract dirt and contamination. Smith and Wesson had been manufacturing cartridge revolvers since 1857. As a matter of fact, they controlled a patent that made them the sole manufacturer of cartridge revolvers until about 1870. Around this time the Russian government approached S&W and offered them a contract for a large order of 44 caliber revolvers. But the Russians stipulated that they did not want their revolvers to fire ammunition with heeled bullets, because of the problem of the soft bullet lube picking up lint and dirt. The Russians stipulated that they wanted a new type of bullet, that would carry the bullet lube in grooves cast onto the bullet, and the grooves should then be pushed up inside the cartridge case where the lube would not contaminate anything. This actually simplified ammunition making a great deal. The bullet could be a simple cylindrical shape of just one diameter. In order to keep the surface of the bullet where the lube was in contact with the rifling, the diameter of the chamber ahead of the cartridge case as well as the diameter of the rifling was reduced, to match the
inside diameter of the cartridge case. So even though the cartridge case was still about .44 in diameter, the bullet diameter was reduced to .429. That is why you will see a step in the chamber of modern revolvers, to transition from the case diameter to the bullet diameter. The new round was dubbed the 44 Russian, and it was the direct ancestor of both the 44 Special and the 44 Magnum rounds. They are simply longer, the bullet and case diameters are all the same.
That is why heeled bullets are obsolete today. The only commercial ammunition manufactured today using heeled bullets is 22 Rimfire. Every thing else has gone to modern bullets that are just one diameter.
Getting back to 'bores'. The convention with revolvers in Cap & Ball days was to call out the caliber of the gun by the bore diameter. The diameter the hole in the barrel had been drilled before it was rifled. But if you measure the rifling grooves of most modern manufactured 44 caliber Cap & Ball revolvers, you will find they are actually 45 Caliber, not 44.
Forget about Period Correctness, whatever that is. A 44 Colt cartridge with a heeled bullet will not work properly in a modern made 44 caliber Cap & Ball revolver. It will be too small in diameter and will not engage the rifling properly, unless you use a hollow base bullet which will expand to grip the rifling. But you are making much more work for yourself than is necessary. That's why all the conversion cylinders made for modern 44 Cap & Ball revolvers take 45 caliber ammunition. It is the correct diameter. You will also find when you start loading your own ammunition that it is much simpler to load with conventional dies than to try to crimp heeled bullets. You don't need any special equipment, all you need is conventional loading dies.
Trust me on this.