Howdy
Yes, when first developed by Winchester in 1873, 44-40 groove diameter was supposed to be .427. However in truth, 44-40 groove diameters were all over the map. They ran as small as .425 and as large as .430 or even more. However .427 was the standard.
I have two old rifles, a Winchester Model 1892 made in 1894 and a Marlin Model 1894 made in 1895, both chambered for 44-40 and they both slug out at .427 on the nose. I also have an Uberti replica of a Winchester 1873, made in the 1980s, and it too slugs out at .427. The '73 was my Main Match rifle for Cowboy shooting for a number of years. I could fire bullets of .427, .428, and .429 diameters out of it with no problems at all. However chambering got a little bit sticky with .429 bullets. The 'large' diameter bullets expanded the necks just enough that they were beginning to have seating problems in the neck region of the chamber. Not so much though that the bolt wouldn't shove them right in when the lever was closed. Since I only shoot Black Powder through that rifle, and since I cast my own bullets for it out of pure, dead soft lead, I decided to size them all to .427. It worked fine, the dead soft bullets may have been 'bumping up' in diameter in the bore, I don't really know.
About three years ago I bought a brand new Uberti replica of the Model 1860 Henry. Chambered for 44-40 of course, I wouldn't own a rifle chambered for 45 Colt. This one, slugs out to .429, which threw a slight monkey wrench into my 44-40 reloading. I am now sizing all my 44-40 bullets to .428. These work fine in the .427 guns, and they do not have chambering problems in the '73 chamber. The .429 Henry seems to like them just fine too, they may be bumping up in the bore to grab the rifling, I cannot say, but even though they are nominally .001 under rifling groove size I have no accuracy problems with them and I get no leading.
When Ruger was producing a convertible model 'original model' Vaquero with both 44 Magnum and 44-40 cylinders, they were using their standard .429 44 mag barrels. At first though, Ruger really screwed up, the chamber throats were way undersized, down around .425 or so with the 44-40 cylinder. This caused terrible accuracy with those early guns, the bullets were squeezed down coming through the chamber throats and since most shooters use modern hard cast bullets they did not bump up at all, so the 'resized' .425 bullets were not engaging the rifling at all. When some shooters had their chamber throats reamed out to .429 or .430, everything was fine. Why Ruger ever supplied such mismatched cylinders to their convertible Vaqueros is a mystery, but eventually they got it right and began supplying cylinders with proper chamber throats for a .429 barrels with the convertible guns.
However this highlighted a different problem. As I said earlier, .429 or .430 bullets in tight 44-40 chambers are not a good thing. Ruger 44-40 shooters discovered that loading .429 or .430 bullets in their 44-40 ammo created the same interference problem in their chambers that I talked about with my '73 rifle. The chambers were tight enough that the 'fat' bullets were expanding the necks of the brass enough that seating the rounds in the cylinders could be problematic. The solution was to either have the entire chambers, not just the throats, completely reamed out a little bit bigger, or use brass that had the thinnest necks possible. Winchester brand 44-40 brass has the thinnest necks of all the brands I have tried, down around .007 thick, vs .008 or .009 for some other brands. This would buy just enough leeway to allow some shooters to chamber rounds with 'fat' bullets.
That is the history of Ruger and 44-40 folks. Besides the fact that they just will not make a New Vaquero chambered for 44-40 because of the rim issue I already outlined, they would most assuredly use their standard .429 barrels, and even if they got the chamber throats correct there would probably be problems chambering rounds with .429 or .430 bullets.
Next question?
P.S. All those of you clamoring for a 44-40 Ruger, have you ever tried reloading 44-40? It can be a bit fussy because of that incredibly thin brass at the neck, around .007 vs .012 or so for 45 Colt. I ain't saying it is impossible, I have been doing it for years, but it can be fussy and your dies have to be set up just right to avoid crumpled necks when reloading 44-40.