Curious about bores and their variations

So I was looking at some interesting reading on Swedish Mausers, and how they have that butt disc plate that will show the bore info and size, and it was interesting to see the variation on them, I am also familiar a little bit on dealing with different sized bores from working on the 303. So I guess I am just curious to see how often bores are varied in size. Was that just a issue with rifles during the 40s and earlier? I would imagine our modern machining tools would keep them on point. Just curious and wanted to chew the fat on it!

Except for the Mausers that purposefully enlarged the bore, I'd suspect that because the same design was made by different governments around the world & by different hands, variations were a natural event from varying degrees of skill and tooling. I can only suspect that as tooling aged and different levels of competency were involved in production, stuff changed.

Pretty sure those discs aren't referring to the bore but rather the throat. As it erodes from firing, the arsenal would inspect it and note the size.

Even with modern tooling/machinery bores will vary. I've .357s by Ruger and S&W that ranged from .355 to .3598.

US manufactures adhere to tolerances that are set by SAAMI https://saami.org/wp-content/uploads...sting-Copy.pdf

That is the maximum allowable variation. Modern stuff tends to be tighter. Older and war time tend to have more variation.

One of the best things about casting is that we can adjust our boolits to whatever the bore likes.

Along with historical manufacturing variances due to equipment and disagreement about 'standards' and wartime exigencies, you get into variances in chamber throat diameter, revolver cylinder throat variances and 'other stuff' that while meeting SAAMI tolerances, are far apart in what bullet style AND diameter works best. Working with lead, soft compared to most copper jacketed bullets requires more attention to those differences. Modern bullet manufacturing, lead and particularly copper/copper jacketed has added much to attainable accuracy/precision in ALL firearms.

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Originally Posted by 725

Except for the Mausers that purposefully enlarged the bore, I'd suspect that because the same design was made by different governments around the world & by different hands, variations were a natural event from varying degrees of skill and tooling. I can only suspect that as tooling aged and different levels of competency were involved in production, stuff changed.

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Why would they purposely enlarge the bore?


So even today we have variations, so a 'perfect' bore is more of a idea than a reality. I just find it interesting to see what size the bore is vs, what size you need for the bullet for good accuracy.

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Originally Posted by TheFlynn01

Why would they purposely enlarge the bore?


So even today we have variations, so a 'perfect' bore is more of a idea than a reality. I just find it interesting to see what size the bore is vs, what size you need for the bullet for good accuracy.

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When they went from the round nose bullet to the spitzer bullet, they enlarged the bore. Why? Who knows, some sort of German logic. That's why there are J bore .318" 8mm Mausers and S bore .323" 8mm Mausers.

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Originally Posted by Nobade

Pretty sure those discs aren't referring to the bore but rather the throat. As it erodes from firing, the arsenal would inspect it and note the size.

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In order to gauge throat erosion there would have to be a depth adjustment on the bore gauges in order to position the gauge in the correct position of the chamber. There is no such tool. There are two threaded rods that the gauges thread into. One is a short rod with no depth adjustment. The second is the rifle's cleaning rod to check the entire length of the bore. These inspections were done at the regimental level and one step up in the army workshops.

http://dutchman.rebooty.com/tools.html

Dutch

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Originally Posted by Dutchman

http://dutchman.rebooty.com/tools.html

Dutch

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Thanks for posting. That's a nice collection of tools.