Colt 45, Ruger Old Model Vaquero

The cylinder is missing! Actually it's only missing from this picture. I know where it's at. It's went Priority Mail today to "Cylindersmith.com" .

Ruger must have had someone asleep at the switch a few years back when they built this handgun. The chamber throats are about 0.448" in diameter. That's interesting because this is a 45 Colt whose barrel rifling major diameter is 0.451".

The bullet exits the cylinder chamber through the cylinder throat (0.448"). At that point the bullet is swaged down to that diameter.
Next the bullet enters the barrel which has rifling grooves of 0.451" diameter. The bullet is now swaged 0.003" smaller than the barrel's major diameter. Can you almost hear it rattling down the bore like a Brown Bess musket ball at Lexington Green?

See the problem there? The bullet will be accelerated and rotated inconsistently from shot to shot. Without a proper fit a bullet cannot "be all it can be" in terms of velocity and accuracy.

The bullet is supposed to be the same diameter as the barrel (or larger) to seal the burning propellant behind it. A copper bullet will be the same diameter as the grooves. A cast lead bullet is more malleable and should be ~0.001" larger so that in can obturate properly to form a gas tight seal.

When a bullet doesn't form a good seal as it transits the barrel not only do velocity & accuracy suffer, but, all sorts of nasty fouling can develop in the barrel -- more than usual. The burning gases can melt the lead as it passes between the barrel and bullet causing "lead fouling." Lead fouling can be a metric son of a gun to remove.

Apparently it's a fairly common problem on this vintage Ruger. Common enough that the Cylindersmith apparently has quite a hobby business going reaming chambers out to better match up with the barrels they feed.

Yes, the cylinder is indeed missing.
Hopefully only for a couple weeks.
Hopefully it will return and show a measurable improvement (reduction) in size of groups shot.

Of course, it's going USPS so there's still a good chance it's the last time I'll see that cylinder.