Howdy
Here is the best I can do for a comparison photo. Top to bottom, 'old model' Vaquero, New Vaquero, Three Screw Single Six. As has been stated, in the not too distant past Ruger was building a reduced size single action revolver chambered for 32 H&R Magnum on the Single Six frame and cylinder. As a matter of fact, I really missed the boat a few years ago. One of the distributors was unloading boat loads of them for $299 each. I should have grabbed a pair for my wife to shoot in CAS. That was the end of them, Ruger has not made the 'Vaquerito' since. But this photo does show the comparative size of the Single Six and the larger frame guns. The 32 H&R version was the same size as a standard Single Six.
As has also been stated, some gunsmiths are customizing Single Sixes into 38s. I know several CAS shooters who shoot them, or the older 'Vaquerito' that Ruger was making. I also know one lady who has a pair of Single Sixes modified to shoot 38 Specials. Very nice little guns, very lightweight with their bored out chambers and 38 barrel. The only drawback is that with the shorter cylinder bored out for 38 Special, one has to watch OAL so the bullets don't hang out the front of the cylinder. I just picked up one of my Single Sixes and compared one of my standard 38 Special, 158 grain Semi-Wadcutter loads to the cylinder. If the cylinder were bored out for 38 Special Chambers, my 38 Semi-wadcutter reloads would poke out the front of the cylinder. Because of this, some shooters load these modified guns with 38 Long Colt ammo instead of 38 Special.
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Regarding 41 Colt, it is a much older cartridge than 41 Magnum. 41 Colt, also known as 41 Long Colt was first introduced by Colt in the late 1870s. Unlike 45 Colt, 41 Colt used a heeled bullet. A heeled bullet is the same diameter as the outside of the case, like modern 22 Rimfire ammo. 41 Colt originally used a 200 grain bullet of about .408 in diameter over 21 or 22 grains of Black Powder in a case about .93 long.
The problem with heeled bullets was that they carried their soft, BP bullet lube on the outside of the bullet, so they could pick up dirt and grit. About 1895 the ammunition makers changed the design of the 41 Colt, changing over to a bullet that slid inside the case like any other modern bullet, sealing the bullet lube in grooves completely covered by the case. The new bullet diameter was about .386 in diameter. In order to engage the earlier larger diameter rifling of the older guns, a hollow based bullet was used that would expand at the skirt to engage the rifling.
The cartridge at the center of this photo is a 41 Colt. On the left is a 45 Colt, on the right is a 44 Colt. Both the 41 Colt and the 44 Colt cartridges in this photo have heeled bullets. You can see how the bullets are the same diameter as the cases, just like with modern 22 Rimfire ammo.