caliber increments

[foresterdj]

Was wondering if there is a reason for the typical caliber increments?
.32 to .36 = .04
.36 to .40 = .04
.40 to .45 = .05
.45 to .50 = .05
.50 to .54 = .04
.54 to .58 = .04
.58 to .62 = .04

I wondered if it might have to do with a number of ball per pound? Or maybe in days of yore, when a rifle was refreshed by boring and new rifling if this much change was needed to be cutting in new material?

[Wingshot]

I don’t know about now but I remember seeing oddball bullet molds as well as some old original rifles that were .38, .43.47, .53 as well as some larger bore sizes being available. I surmise that in the modern world of barrel making it’s the tooling that sets the standards for the gap in bore sizes. Just my humble opinion.

[Hank01]

Interesting observation but is there a definitive answer? Perhaps one of the many mysteries of the world of firearms that defies a definitive answer. But, calibre denotes the bore diameter whereas  a smooth bore (was) is "gauged" by the number of balls per pound. As i see it "standardized" calibres didn't really take hold until the metallic cartridge gained favor.

Hank

[D. Taylor Sapergia]

In their period, all guns were described by their "number of balls to the pound" or gauge, more frequently than by the bore diameter in thousandths of an inch.  Calibre, or decimal description is more of a modern thing.  And today, we obsess on decimal description as it makes discussion on ball dia. and patch thickness more conclusive. I may be in error, but I don't think 18th C people were concerned about whether they had .018" linen or .020" linen, though Hawkeye was apparently aware that silk gave him another 40 yards.

[RAT]

You listed modern standardized calibers. That didn't exist before modern 20th century production of muzzleloading barrels. Modern makers, using modern machines and tooling, need to use industry standard calibers to keep costs down. You could probably find a barrel maker today that will make an "off" caliber, but it will be a custom order.

Calibers before modern machine production would be determined by whatever reamers the maker had available... or made himself. These could vary widely.

[Pete G.]

Look at balls per pound and I think you will see a pattern.

[foresterdj]

So ball per pound for these calibers (column D) does not leap out to me as an obvious reason. I suppose the one comment that it is just a modern equipment standardization thing is the most likely.

[Daryl]

When I read through the book: "Firearms of the American West 1803-1865" I read reprinted orders by the gun stores in the West to the gun makers in the East for rifles and smooth rifles,
they were distinguished by "balls to the pound" (usually47 to 32 to the pound - .46" to .53") rather than calibre in inches. The smallest ordered were in the range of 180 to the pound (.29")and anywhere in between there and 47.
Seems to me, the rifles were ordered to "use X # balls to the pound", not that the calibre was in "balls to the pound".  That might not be correct, though..
This designation was quite possibly a holdover from their British etc Heritage.
Strange, but the Army's Muskets (mostly of basic French design) used were called by calibre, ie: .69 & the military rifles as well, seems to me in inches, .54 to .58.

[foresterdj]

That would be reasonable too I guess, since the earlier in time guns were all smoothbore; rifling being a later advent, describing them by the bore system of ball per pound was likely common place.

[foresterdj]

So I worked the numbers backwards from my previous spreadsheet, setting balls per pound as the entry, calculating weight of those balls in lead, the spherical diameter, and then since it worked out better for common calibers added .005" (so the resulting ball would be .005" under bore diameter) and got these. Actually, as ball per pound got larger, due to rounding, there was a range of numbers yielding the same caliber to the 1/100th. Anyway, the common (?) calibers could be expressed by a reasonable whole number of ball per pound as shown below. Though still curious why we ended up with calibers like .36, .40, .45, & .50; instead of .35 (115/lb), .41 (70/lb), .46 (50/lb) or .49 (40/lb), which seem to be also nice whole numbers of ball/lb.

Like the number of licks to the center of a tootsie pop, the world may never know.

[foresterdj]

What the heck is "json parser validator", I did not put that into my posting.

**I removed it. It some jiberish that often is added by the photo hosting site** Dennis

[T*O*F]

If you take fractional sizes and convert them to decimals, you will find that many of them match standard calibers.  Perhaps it is all about available, standardized tooling.  At some point in time, I'm sure high volume barrel makers switched to commercial gun drills rather than making their own.  How far back does the fractional system of measurement go.

[Daryl]

This is my chart.
Just noticed:
 the phone #  no longer in use.

[RAT]

I think you're trying to connect oranges to a suspension bridge (that's a Big Bang TV reference). Before cartridge firearms, small arms projectiles (round balls) were referred to by the number of balls per pound of lead. The actual diameter was incidental to that. For example... so many balls of an APPROXIMATE diameter would weigh a pound. But they didn't split hairs. In other words, 32 balls to the pound might not equate to every ball measuring a specific desired diameter within a thousands of an inch. The actual diameter might vary widely. That's why a mold was often supplied with the firearm. Patch thickness could be changed depending on how tight the shooter wanted the load to be. The HBCo referred to this variance in diameter as "windage". They supplied balls of a size that would fit different guns... by different makers... all of supposedly the same bore size. That's because the actual bore size varied so much.

The consistency in decimal variance between commonly offered modern muzzleloading calibers is a modern thing.

You might be able to find a barrel maker that will make you a .52 cal... or a .43 cal... or whatever. You might also find someone to make you a mold in that caliber. But you're probably not going to find ramrod accessories... off the shelf... that will work. Industry standards have developed over time to make this easier and more cost effective for everyone.

Oh... and rifled barrels are almost as old as firearms themselves. Here's a rough timeline...

1483-1499   Early wheel lock invented in Italy
1500-1520   Wheel lock adopted by German gunmakers
1540-1550   Rifled barrels are developed in Germany
1540-1660’s   German “cheek stock” in use
1530-1550   Shoulder stock developed in France
1600-1625   Overall length of German “cheek stock” rifle is 48”-50”
1625      Overall length of German “cheek stock” rifles shortened to 40”
1615-1630   Flint lock developed in France
1660’s      French shoulder stock adopted for German rifles
1730’s      Mass immigration to Pennsylvania by German immigrants

[WadePatton]

You listed modern standardized calibers. That didn't exist before modern 20th century production of muzzleloading barrels. Modern makers, using modern machines and tooling, need to use industry standard calibers to keep costs down. You could probably find a barrel maker today that will make an "off" caliber, but it will be a custom order.

Calibers before modern machine production would be determined by whatever reamers the maker had available... or made himself. These could vary widely.

 In fact, Mr. Burton of FCI Barrels, has a few "odd" ones in his listing. I've always wanted one, but I have some standards to finish up first!   He had 30, 38, 47, and 52 on the list last time I looked. Well I do have his 30 already. 

As far as the troubles involved: I see casting balls as part of the process and Tanner will cut a mold any size, no extra charge. A tow worm covers many calibers. Shoot well and have fun!

[foresterdj]

Some interesting discussion and speculation. Indeed, every possible balls per pound will correspond to some diameter. And quite likely(?) the ability to measure to the 1/1000th precisely, and the obsession to do so, is a modern thing. Certainly, a standardization for tooling purposes in manufacture took place.

Though, all this could have lead to any infinite number of "standard" calibers. Somehow we came to have the more currently expressed array, .32, .36, .40, .45, .50 etc., instead of .33, .35, .39, .49, or even .25 (1/4"), .3125 (5/16"), .375 (3/8"), .4375 (7/16") and .50 (1/2") etc.

So somehow it came to be. Unimportant, I guess. Perhaps my initial question was not why we have the calibers we have (since we could have had any calibers attain common usage), but why would we have settled on the size increments from one size to the next?

[hanshi]

Like most factories today it is much simpler and cheaper to standardize these calibers we have now.  So called "odd" calibers fall into the custom realm.  That, IMHO, is at least one reason for the numbered calibers that are standardized. 

[Dphariss]

Originals were either forge welded and then bored, long bit reamed and rifled or they were drilled, reamed and rifled starting the the 1830s +-. Boring from a a bar made standard calibers a little easier but even in brass suppository rifles of the late 19th c BP era the bore sizes were only held to about .010” tolerance. As RAT stated there was no standard calibers in ML arms. But in the West, meaning West of Westport Landing, balls smaller than about 40 to the pound were not considered sufficient. In the East, when there was still a lot of big game calibers were 44 caliber maybe 60 to the pound or heavier. And most were under 30 to the pound if the people making the statements were correct. Hanger I wonder about sometimes but he WAS there at the time and he as a rifle guy.
32, 36, 40, 45, 50, 54 are “standard” modern calibers as are 58, 62, 69.  But gun drills and reamers for barrel work are generally custom made to a specific size.
Prior to the used of the gun drill the forging was bored and reamed until it cleaned up. Then it was rifled. If it came out 43 or 45 the maked just made a mould to match.

[Dphariss]

Some interesting discussion and speculation. Indeed, every possible balls per pound will correspond to some diameter. And quite likely(?) the ability to measure to the 1/1000th precisely, and the obsession to do so, is a modern thing. Certainly, a standardization for tooling purposes in manufacture took place.

Though, all this could have lead to any infinite number of "standard" calibers. Somehow we came to have the more currently expressed array, .32, .36, .40, .45, .50 etc., instead of .33, .35, .39, .49, or even .25 (1/4"), .3125 (5/16"), .375 (3/8"), .4375 (7/16") and .50 (1/2") etc.

So somehow it came to be. Unimportant, I guess. Perhaps my initial question was not why we have the calibers we have (since we could have had any calibers attain common usage), but why would we have settled on the size increments from one size to the next?

Maybe because thats what Douglas was making in the 1960s?

[yulzari]

I will not argue with the arithmetic but all the very old 0,32” muzzleloader rifles I have seen were described as 140 bore.

[Daryl]

140 balls to the pound is .322".