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How did the bore diameters like say .54 become established ?

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I was pondering this question and wondering how these what seems like random bore diameters became established. Was .54 established from freshing out original bore diameters in 50 cal. a time or two ? I would think original calibers would have started life in even tenths as in 30 cal bore becoming .32 and .36 when freshed out, 40s becoming .42 and.44 and .50s becoming .53 and .54, 60s becoming .62 and etc.
I've read original Hawkens were often made in .52 and .53 when measured but this too could have been freshed out measurements taken of original guns in modern times.
The freshing out process does not require a rifling machine as one is reaming out the corroded/eroded bore and using whats left of original grooves to track the scraper in making them deeper into fresh metal. As most rifling was originally quite deep (.012 and deeper) by modern standards, it is conceivable/ likely that these new calibers would be established and when advantage was experienced in their usage of power, efficiency and accuracy they could have became established sought after calibers cut in new/original barrels.
As a side note it must be remembered that as far as Hawken rifles go many were made in calibers smaller than .50 before the brothers moved to St. Louis.
 
Freshing seldom increases calibers more than 2 calibers, like .50 to .51. It would take me more than 2 full days to fresh a barrel and increase the bore by 2 calibers. Many originals have breechplugs not much bigger than bore diameter. For example a .50 might have a plug not much bigger than 9/16”. Large increases in caliber would often require making a new breechplug and re-threading the breech. Often they would rather cut off the powder chamber and take an inch off the muzzle as well, allowing use of the same breechplug.
 
Freshing seldom increases calibers more than 2 calibers, like .50 to .51. It would take me more than 2 full days to fresh a barrel and increase the bore by 2 calibers. Many originals have breechplugs not much bigger than bore diameter. For example a .50 might have a plug not much bigger than 9/16”. Large increases in caliber would often require making a new breechplug and re-threading the breech. Often they would rather cut off the powder chamber and take an inch off the muzzle as well, allowing use of the same breechplug.
Good point Rich I had not considered the breech plug diameter.
 
Freshing seldom increases calibers more than 2 calibers, like .50 to .51. It would take me more than 2 full days to fresh a barrel and increase the bore by 2 calibers. Many originals have breechplugs not much bigger than bore diameter. For example a .50 might have a plug not much bigger than 9/16”. Large increases in caliber would often require making a new breechplug and re-threading the breech. Often they would rather cut off the powder chamber and take an inch off the muzzle as well, allowing use of the same breechplug.
Does Hoyt consider breech plug diameter as a limiting factor or only barrel diameter when boring and re-rifling to a new caliber ?
 
Another consideration is that many decisions on the "caliber" of older rifles is based on measuring the muzzle. Lots of those guns were coned with files in such a way as to appear to be the same as the inner bore. A 50 caliber bore could measure 54 or 53 with the coning so carefully filed in as to seem to be the final bore size.

Just spit balling here.
 
Another consideration is that many decisions on the "caliber" of older rifles is based on measuring the muzzle. Lots of those guns were coned with files in such a way as to appear to be the same as the inner bore. A 50 caliber bore could measure 54 or 53 with the coning so carefully filed in as to seem to be the final bore size.

Just spit balling here.
Another point I had not considered. Good stuff guys! I love kicking around notions and hearing different prospective and ideas!
 
Does Hoyt consider breech plug diameter as a limiting factor or only barrel diameter when boring and re-rifling to a new caliber ?
Of course, but modern breechplugs are often much bigger than bore diameter. So, a .50 with a 5/8” plug could go all the way to a .58 without issue with the breechplug. If the barrel itself would be considered safe at whatever bore is desired.
 
Does Hoyt consider breech plug diameter as a limiting factor or only barrel diameter when boring and re-rifling to a new caliber ?
Obviously breech plug diameter can be a limiting factor, but having spoken to Mr Hoyt about reboring some contemporary barrels, the depth of any dovetails or tapped holes is a big concern, say on a TC barrel for example.

I just cut shallow tenon dovetails into a 62 caliber swamped barrel with deep radius rifling. Across the flats measures under .900” in the middle of the barrel. Imagine nothing more than a ‘light’ refreshing of the bore would be possible if it ever became necessary. Then there is the breech plug, while I forget the thread size at the moment, and I am not going to check, the flat at the bottom of the tapped hole in the barrel doesn’t cover the bottom of the rifling by much. Strike two to the thought of a future rebore.

I don’t think general statements can be made about reboring size limits, as each barrel brings its own set of conditions. Now if one is insistent on a general rule, it would have to be something like ‘sometimes, always, never’.
 
When rifles were ordered to be built by the Pa. and other gunsmiths , the official govt. cal. was .457. Before 1800 that was raised to .480. The first Harpers ferry muskets , were .540 cal.. Musket calibers in France were .69. Britian were .75. Both those smooth bore cal.'s influenced American muskets , with the French .69 having the most influence. By the American Civil war , the French Minnie Cal. .58 was in vogue. That stuck until ctg. calibers took over.. That's my opinion , to best of my knowledge.
 
Probably after hundreds of years of shooting round balls at humans and wild game and observing the lethality, consensus was formed on the "right" or "adequate" calibers.
 
Wouldn't the ball size be dictated by the bore not the other way around ? I'm wondering how the random bore size became established.
I think you’re assuming they WERE established at some point. The question is when, and whether you mean “established” or that certain sizes were common. If talking trade rifles, yes, orders specified this or that balls to the pound. Same with any military “model”. But for one-off custom long rifles, the maker normally purchased barrels pre-bored and often pre-rifled. We can guess that in most cases barrels made and bored in boring mills were bored out to a number of standard calibers. After all they didn’t want to make a new drill every time. Reaming doesn’t take much off very quickly but adds to variation, because they reamed until it was clean and bright end to end.

Even as early as the 1770s gunsmiths in Pennsylvania were getting barrels pretty much ready to use, though some needed to be rifled.

You mentioned Hawken rifles. By then barrels were being made by the thousands, and I’d guess they could request blanks that were bored and ready to rifle in calibers that were popular in the day. Smaller for the local guns and larger for those going west.

In the black powder revival days, machinist trained guys started making barrels in what we think of as standard calibers. .32, .36, .38, .40, .45, .50, .54. The .38s dropped out in time. Really big caliber barrels like .58 and up seem to have come about in the 1960s on.
 
As @rich pierce states above, bore diameters were established and identified by the number of balls per pound they shot. A 32 ball per pound barrel would measure out at about 0.535". Precision measurements by micrometer didn't become commonplace until about 1850 although some earlier micrometers were in use for inspection rather than development and design of tooling.

Most of the bore diameters we are familiar with have corresponding regular balls per pound increments. A 36 caliber bore is about 100 balls per pound. The balls per pound description is more important to a hunter or artificier keeping troops supplied with ammunition than bore diameter.
 
Old Turner Kirkland of Dixie Gun Works fame used to publish a theory in the back of his catalog. He thought bullet gauge (bullets per pound) was chosen by ratios of 1/2, 1/3,1/4 or 1/5 starting with the popular musket sizes .72 (12 per pound) or .69 (14 per pound).

For example, 1/2 of a .69 (14 gauge ) is .54 (28 gauge). It doesn't always work out but is interesting to think about.
 

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