Pre-war/Post-war bore diameter variation

[DCWilson]

I got a set of Brownells range rods to make sure timing was good on all my revolvers, some of which are fairly old. I was unable to get the head down the bores of two guns -- a .38/44 Outdoorsman that was shipped in 1933 and a .38/44 Heavy Duty Transitional that letters to 1946. On these two guns the head slipped into the barrel only a fraction of an inch and went no further.

There was no problem with a .38/44 Outdoorsman Model of 1950 (Pre-23, shipped 1956) nor with a .357 Magnum Revolver (Pre-27) also from 1956. The rod moved smoothly with no play up and down the barrel and cylinder chambers.

The rifling, particularly in the HD, seems a little more pronounced than I see in barrels today. Can anyone tell me if land diameters in pre-1950 guns were tighter than in later years? I'm just not sure how to think about what I have found.

The barrels in the older guns look clean and shiny. I was surveying the guns in preparation for firing them, but now I have my doubts.

David Wilson

 

[DCWilson]

I got a set of Brownells range rods to make sure timing was good on all my revolvers, some of which are fairly old. I was unable to get the head down the bores of two guns -- a .38/44 Outdoorsman that was shipped in 1933 and a .38/44 Heavy Duty Transitional that letters to 1946. On these two guns the head slipped into the barrel only a fraction of an inch and went no further.

There was no problem with a .38/44 Outdoorsman Model of 1950 (Pre-23, shipped 1956) nor with a .357 Magnum Revolver (Pre-27) also from 1956. The rod moved smoothly with no play up and down the barrel and cylinder chambers.

The rifling, particularly in the HD, seems a little more pronounced than I see in barrels today. Can anyone tell me if land diameters in pre-1950 guns were tighter than in later years? I'm just not sure how to think about what I have found.

The barrels in the older guns look clean and shiny. I was surveying the guns in preparation for firing them, but now I have my doubts.

David Wilson

 

[john traveler]

Throughout the long and glorious production history of S&W revolvers in the 29th century, barrels were made by forging, deep hole drilling, reaming, and broaching. There is bound to be some production tolerance variations due to re-sharpening of cutting tools.

I slugged a .38 S&W Victory model barrel once and was surprised to find that the groove diameter was the same as that for an M&P .38 Special barrel. This was at a time when established reloading manuals such as Lyman's 45th stated that .38 S&W barrel dimensions were some 3 to 5 thousandths larger than .38 Special!

We already know of S&W's penchant for not discarding any parts. By extension, we can also surmise that maybe they never discarded any tooling either.

 

[DCWilson]

Thanks, John. I am going to have to slug the barrels on my HD and the early OD to see exactly what I have. The front openings of the cylinder holes mike at .356, and the range rod head (.350) enters easily. To the extent that my poor close-up vision permits me to measure land-to-land diameter, I seem to be looking at .349 to .350 at the muzzle. That seems pretty tight to me.

DW

 

[tomcatt51]

Originally posted by DCWilson:
Thanks, John. I am going to have to slug the barrels on my HD and the early OD to see exactly what I have. The front openings of the cylinder holes mike at .356, and the range rod head (.350) enters easily. To the extent that my poor close-up vision permits me to measure land-to-land diameter, I seem to be looking at .349 to .350 at the muzzle. That seems pretty tight to me.

DW

Not really a bad thing at all with lead bullets if the major (groove) dia is appropriate , ~.357. How are you measuring the throats (The front openings of the cylinder holes)?

 

[DCWilson]

Digital calipers. I just kept taking readings until I couldn't get one any larger.

DW

 

[tomcatt51]

Originally posted by DCWilson:
Digital calipers. I just kept taking readings until I couldn't get one any larger.

DW

Dial or digital calipers are usually not adequate for the task. Pin gauges work but can be mileading if the throats are out of round. A telescoping gauge and a micrometer that will read tenths (.0001") seems to work best.

 

[john traveler]

Tom is correct. Dial or digital calipers are not quite up to the task because the thickness and positioning of the caliper prongs can make a significant difference between your measurement and what it really is.

Without access to a set of pin gages, the next best is to push soft lead slugs through the chamber throats and measure with a micrometer.

 

[DCWilson]

Tom and John -- Thanks. I learn something new here every day. I don't have the proper tools, so I'll just push slugs through and measure them.

David

 

[BlackAgnes]

How do you guys accomplish this measurement with S&Ws five lands and five grooves? Wouldn't a land always be opposite a groove?

I've always wondered.

Tim

 

[john traveler]

Determining groove diameter on a 5-groove slug is black magic. You either need a special micrometer or a standard micrometer and special vee-block with conversion formula.

A poor man's way would be to use the hole gage (counterpart to the plug gage): a plate with precision size holes drilled/reamed in it. The slug will pass thru a slightly larger hole, therefore the size must be the next smaller size. A variation of this is to make several bore slugs and press them thru a bullet lube sizer. The barrel slug will come out with the least distortion in the correct sizer.