When I bought my first Old Model Vaquero in .44-40, the chambers were so tight and not uniform that I could not easily chamber factory loads! In addition, the throats were .425" in diameter! I finally persuaded Ruger (along with some help on similar problems by Duke Venturino, et al, in print) to do something about it. I sent the gun back and they did, indeed do something, either reaming or replacing the cylinder. HOWEVER...they left the .425" throats! The groove diameter of the barrel is .429". I was going to have the throats reamed out, but decided to try shooting hard-cast bullets of .430", just to see what would happen. Naturally, I assumed that accuracy would be horrible. But, when I did some testing, by shooting from a sandbag rest at 25 yds, I found the gun would group 1-5/8" 5-shots consistantly! How was/is this possible? I used hard (BHN 17-22) cast bullets. Although I have not removed the barrel to prove my theory, I believe that the hard cast bullets squeeze down going through the throats. But the internal compressive stresses in the bullet matrix do not have time to dissapate (in the form of heat) in the time the bullets pass through the throats, so, when the bullet hits the forcing cone of the barrel, it re-expands! Excited by these tests, I procured another .44-40 cylinder with the looser chambers and the .425" throats, which was fitted to another OM Vaquero originally in .44 Magnum. (I had a .44 Magnum cylinder fitted to the first gun, giving me a pair of convertables.) Accuracy in the second gun is also very good, considering it has a 5-1/2" barrel instead of the 7-1/2" on the first gun.
Hence, I have no intention of reaming the throats of the .44-40 cylinders. The secret is to use hard-cast bullets.
(Note: in spite of the accuracy of these guns, that does nothing for the speed of my shooting! That is pretty slow, and may be getting slower with my age!)