To understand why the .38 Special is a .357 and the .44 Special is a .429, you have to go back to the Civil War. Revolvers in those days were what we call "cap and ball" today, and could be loaded with loose powder, a separate projectile and ignited with a percussion cap.
To make such a revolver, the chambers were drilled from the front, leaving a wall or floor at the back of the chamber. A smaller hole was drilled from the back and threaded for the nipple.
To load such a revolver, point it up, fill a chamber with powder, seat a ball and ram it down. The ball had to be a tight fit and most revolvers had a compound lever mounted under the barrel. A properly sized ball left a thin ring of lead after rammimg. This means the ball, chamber and groove diameter of the barrel were all the same size -- they had to be.
After loading was complete, the chamber mouths were filled with grease -- lead bullets must be lubricated, especially if used in rifled barrels -- and the nipples capped.
After the Civil War, metallic cartridges were the wave of the future. A brass or copper case, containing a primer or priming mixture was filled with powder and a bullet crimped in the case mouth. This made a tight, rugged waterproof package that could be loaded more quickly than the old cap-and-ball arrangement. To make such a revolver was simple -- just bore the chambers all the way through, add a loading gate on the recoil shield, and reshape the hammer to set off the primer.
But wait! If the cartridge case goes inside the chamber, and the bullet goes inside the case, then the bullet must be smaller than the barrel! It won't shoot accurately.
The solution to this was the heeled bullet -- the cylindrical bullet had a reduce-diameter base (the heel) that fit inside the case. The rest of the bullet was left groove diameter. And the grease was smeared on the bullet.
And the grease picked up grit and crud, dried out in the sun, got rubbed off when carried in the pockets and so on. Back to the drawing board. The new bullet was made the same size as the original heel, with grease grooves and seated in the case deep enough so the grooves were below the case mouth. This is called an "inside lubricated" bullet and is the answer to the problem -- inside lubricated bullets are the standared for lead bullets to this day.
But now the bullet is too small for the barrel. There were two choices -- make the bullet, case, chamber, cylinder and revolver frame all bigger, or just make the barrel smaller. The latter was the obvious choice.
The .38 was reduced to about .36, the .44 (which was closer to .45 in the original heeled bullet) to about .43. But they retained their original caliber designations and were offered with soft lead bullets with hollow bases, which would still shoot passibly well in older revolvers with the larger bores.
