My 44-40 is an original Ruger Vaquero stainless. The throats pin gauge at .429 at the cylinder mouths and taper back to .4305 at the chamber mouth. The groove diameter is .429. I load with a Lee TL 430-240-SWC or the Lyman 429360 (245 gr SWC). I size them at .429 and lube with BAC. I load the Lee's over 6 gr 700x for 950 fps and the Lyman's over 8.5 gr Unique for 1060 fps (out of the 7 1/2" barrel). Both are very accurate and last time out I shot 100 rounds shreading 10 pop cans bouncing them from 15 yards all the way out to 70 - 90 yards with no leading.
I have taken the 44 magnum cylinder out of my 50th Anniversary FTBH and it drops right into the Vaquero. Fit and timing are perfect. The same Lee bullets loaded over 8.5 gr Unique hit to the same POA and are just as accurate.
Attachment 205319
With the 44 magnum FTBH cylinder;
Attachment 205322