I'll float my stick with Sir Charles! My OM Ruger Vaqueros still have .425" throats and I shoot .430" bullets (the chambers are large enough in the mid- 55-XXXXX and 56-XXXXX range to accept Winchester brass loaded therewith). When my old eyes are co-operating I can get 1-5/8" groups from the 7-1/2" gun at 25 yds hand-held from the bench. I use hard-cast (BHN 15-22) commercially cast bullets and smokeless powder loads.
So far as Colt's Single-Action pistols in .44-40 are concerned, the only experience I've had is with an original Colt's Frontier Six Shooter. The original cylinder that throats measuring .4245"! While the barrel was .427" in the grooves. Rather than modify the original cylinder, I ordered a modern steel cylinder which John Kopec was selling at the time, with .427" throats. I shot .428" bullets in that one, again with light smokeless loads. While I can't recall the group sizes, they were about as accurate as any handgun, in spite of having only a 4-3/4" barrel!
Interestingly, a 2nd Generation .44 Special Colt's (supposed bullet dia. .429") had a groove diameter barrel of .427"! The .44-40 is a great cartridge. It is too bad that various manufacturers at various times, including today, couldn't get specs consistant. (The use of .429" .44 Magnum barrels in .44-40 is a manufacturing/economic concession.)