Howdy, Pards,
The case coloring on the blued OM Vaqueros is just that...a chemical coloring. There have been instances of this producing surface rust even without much use.
The subject of the .44-40 OM Vaqueros can get a bit complicated. Originally, Ruger chambered and throated the .44-40 guns according to an obsolete SAAMI bullet specification, which calls for .424-.427" bullets. Yet Ruger used .44 Magnum barrels with nominal groove diameter of .429-.430", which made sense from a production standpoint. Guns with serial numbers starting in the #55-00001 thru about #55-56XXX or so, had chambers so tight that cartridges with .429-.430" bullets wouldn't chamber. Somewhere around the #55-56XXX or so (even Ruger isn't sure exactly where), they did enlarge the chambers so that Winchester brass with .430" bullets would chamber. HOWEVER, they left the throats at .425". Normally, this would be considered a totally bad setup, and most folks believe it. After all, if you squeeze a larger bullet through a smaller throat, the bullet should be sized down to the diameter of the throat. BUT...I have found that if you use HARD-CAST bullets in the BHN 17-22 range (which most commercially cast bullets ARE), the compressive stresses in the harder metal do not disappate in the form of heat. Since the bullets spend so little time in the throat, the residual stress cause the bullet to "pop" back out. I have gotten excellent accuracy, with very little leading in my match guns. (The 7-1/2" barreled gun will get 1-5/8" groups at 25 yds from a sandbag rest! The 5-1/2" gun is not quite as accurate, mostly due to the shorter sight radius.) When purchasing .44-40 OMV's, I always check for the looser chambers with the .425" throats! It should be noted that just before discontinuing the .44-40's, Ruger opened the throats up to .431". Those guns will probably be in the #57-XXXXX series.
I'll pass on this one, however, as I don't want to be a hawg about it! BTW, NEVER TRY TO SHOOT .430" JACKETED bullets through the tight throats! If I need jacketed bullets, I'll switch cylinders which I had fitted to the guns, and put in the .44 Extra Long Russians (.44 Mangle-em to the uninitiated)!
Happy Holidays, Pards!