chamber mouth sizes

[M. De Land]

I've noticed that on several (really used) used guns I've picked up that often as not the chamber mouths are smaller than the groove diameter of the barrel which has never made much sense to me.
This was so on the 62 Police, Navy Arms ( made by Uberti)I picked up a couple years back.
Accuracy was so-so at 25 yards with .375 balls so I finally reamed out the cylinder mouths to .379 and have yet to try it out with .380 diameter balls cast up.
I'll get to it one of these days and post the results.
Any way, I have noticed this inversion of chamber mouth to groove diameter several times in various makes of reproduction guns and am curious about the reasoning.

 

[bob308]

every one I have done has shot a lot better. I have done mostly remingtons.

 

[nkbj]

M.D.
To make matters even goofier the chambers are being taper reamed so unless the ball is kept at the front of the cylinder your accuracy is liable to suffer due to a further reduction in ball diameter.
When using bullets with the rear end sized to slip into the chambers it can get to being a pain in the rear end.
Another problem with the taper reaming is that depth of reaming is not always adequately controlled to be consistent from chamber to chamber. Then because it's a conical cross-section instead of cylindrical both the volume from chamber to chamber and the bullet diameter (be it long or short bullets) are affected.
A little laxity on the quality control ends up making a big difference in performance.

 

[Long Johns Wolf]

I guess the reasoning back in the 19th century was the makers like Colt did not trust their steel. Hence the oversize rifling groove dia vs. chamber mouth. You get a lot of gas leakage and the balls are kind of rattling down the barrel. But the soldiers back then were supposed to use their percussion revolvers to shoot volleys. Accuracy of handguns was not the major concern of the military strategist.
In the 20th century the raplica makers just copied what the original makers did in the 19th century ... with few exceptions like Belgian FAUL's Centaure. These Belgian Colts were constructed like modern target revolvers with the rifling grooves adjusted to the dia of the chamber mouth.
Pietta followed this only a few years ago. To the best of my knowledge Uberti is still sizing their .44 cal. revolvers to ca. .446" chamber mouth vs. ca. .451" rifling groove dia.
Long Johns Wolf

 

[rodwha]

What I've read all too often is quite the opposite. Pietta's generally have 0.446" chambers (my 2013 did) and Ubertis have 0.450" chambers. Both with 0.452" bores.

 

[curator]

MD:

Every original cap & ball revolver I have had the occasion to measure had chambers slightly larger than groove diameter of the bore. If you are willing to spend extra for the "shooter's model", you can buy a modern replica made correctly. My original 1851 Colt "Navy" has .375 groove diameter and chambers are bored .3775-.378. The bullet mould that came with casts a .382" diameter ball and a short conical with a .375 diameter "heel" and .383 top-band. In some of Sam Colt's original publicity writing he stressed the fact that the ball gets sized down progressively, first by loading it into a slightly smaller chamber, then again as it enters the bore. His claim was that the ball being oversize and getting swaged down made his guns "shoot harder' with the same amount of powder compared to the "revolvers" of the day (Allen & Thurber Pepper-boxes)

 

[M. De Land]

Yes, I have also noticed that chamber mouths in the same cylinder are not the same diameter and often are not round.
It was obvious out of round in some chambers in the 62 police I reamed as there were spots in one or more of the chambers that remained blue after the reaming.
I suspect this is happening from factory practice of gang reaming all chambers simultaneously. Any reamer oscillation in the fixture would cause it and individual reamers are sharpened periodically changing the diameter slightly chamber to chamber.

 

[nkbj]

Heh, got one cylinder... you can pull it out of the revolver, set it on the table and looking down at it see the different chamber depths. Definitely a candidate for developmental design and rework.
Tell you the truth though I've always been skittish about making the chamber walls on the .44's any thinner. But oh well, it's worth a try.