Beginner Question # 1 - caliber and scale

[jaxenro]

Looking over some of the various mini (1:5 - 1: scale barrels I see it seems they are made to specific caliber more then scale caliber. I am guessing this is due to readily available components for firing in smaller sizes (.50, .69).
Using a civil war Napoleon smoothbore as an example a 11" barrel would be really close to 1:6 scale (11" x 6 = 66" which is the quoted length for many Napoleons) yet Brooks 11" Napoleon, for one, is .50 caliber while scale would be about .77 (.77 x 6 = 4.62)
 
So my question really is there a reason for this? Even .69 caliber in the 11" size would be closer to scale, .75 would be even better and almost not discernable (try to eyeball a fiftieth of an inch difference between .75 and .77). Is there simply not enough metal in the smaller barrels to not make them safe to bore out to a larger diameter?

[subdjoe]

My uninformed WAG is that since there are already barrels being produced in .50 caliber it is a matter of economy of scale.  Buy up, or produce, the stock and set aside some for making small cannon.  Keeps production costs down, which helps keep prices down. 

And, as you mention, ball and cleaning brushes and the like are readily available.

[Doc Brown.]

Looking at pictures of original James rifles and Napoleons they would look to have bores larger than the 1 caliber rule would allow for. You have to figure them were to fight a war and safety wasn't there only concern. If your looking for an exact scale model the only one I can think of would be Scale artillery and there website says they wont break the 1 caliber rule. Maybe if you vent it he would. Just have to ask.
 
UPDATED
I just looked at the scale artillery barrel in the sickies and I'm wrong about the Scale artillery barrel being scale model. The trunnions are way off. Scale model would have integral trunnions and look way different.

[GGaskill]

Most bronze tubes are under the 1:1:1 rule but you have to consider weight was important in regards to transport and deployment, and bronze guns had a relatively short service life; they were retired after 500 rounds which kept them out of the fatigue failure regime.

[jaxenro]

ok so what is the 1:1:1 rule? I will look in the stickies and try to find it - pity the search function doesn't work

[seacoastartillery]

     Jaxenro,     The 1:1:1 Rule refers to the fact that your cannon's metal thickness,  looking at a section view which divides the cannon's mass into two equal halves longitudinally, should be equal to the bore size both above and below the bore.  In howitzers and mortars the chamber diameter is considered to be the bore dia. per the 1:1:1 requirements and the metal forward of the chamber can be much thinner than it is around the chamber.
 
      As far as scale goes, you are correct, in most cases the consideration of cost weighs heavily in calculations of material selection.  In our case, with the recent production of rifled sleeves for those who want to line their smoothbore cannons, because of cost, we are limited to sizes which are available by quarters of an inch in most cases.  We make Exact scale re-creations of Civil War cannon, but the fact that a standoff scale cannon can be had for a mere fraction of those prices is not in dispute.  By standoff scale we are talking about a replica of the 1850s, arsenal made, field rifle made by using the plentiful M1841 bronze field gun with was then rifled using the 3.67" bore without modification to produce a 12 Pdr. conversion rifled cannon.  The 1/3 scale replica would use our 1.0000" bore size rifled sleeve instead of a mathematically correct, 1.2233" bore size. 
 
      There are two significant benefits of going along this route, one is price which is about four times less than the exact scale replica and the second is a slightly smaller bore size allows your cannon to retain a little more weight which is beneficial toward recoil control. The original tube on the M1841 bronze field gun weighed 880 pounds.  The method for determining your 1/3 scale tube's weight is to divide the original tube's weight by the cube of the scale divisor (880/3x3x3) = model tube weight.  880/27  =  32.59 Lbs.  From our extensive experience with firing 1/6 scale seacoast rifles which are almost the same, weight-wise, as 1/3 scale field rifles, we have come to consider 45 pounds to be the minimum weight for effecting controllable recoil in 1.0000" bore, rifled cannon, which fire 6oz. to 8 oz. projectiles. In our case, with the 1841 bronze field gun conversion rifle, the weight of the carriage will easily add the requisite weight and the total should weigh between 55 and 65 pounds and have the ability to control recoil.
 
 Tracy & Mike
 

[jaxenro]

Thanks for the excellent answer. So simply put a .5" bore would go in a 1.5" giving a .5" metal, .5" bore, .5" metal cross section.
 
So using 1:6 scale as my standard this would assume my mythical .77" 12 pounder would require a barrel diameter of 2.31", a 6 pounder about 1.83" (assuming a .61" bore), and a 3" rifle 1.50".
 
Although I know nothing about black powder cannons these seem conservative for steel barrels for these smaller calibers (say under .75" down to .50") and even so for brass. For instance many .50 caliber black powder pistols use a 1" barrel and even a black powder 12 guage barrel is unlikely to measure 2" across.
 
I am assuming that as the size of the bore increases both the mass of the projectile and powder increase dramatically as well. So a 1.0" ball doesnt weigh twice a .50" ball but the cube of .50? (A 1" cube of lead weighs 8 times a .50" cube of lead as it contains 8 .50" cubes, not sure how this relates to round shot but it must be similar) so is this a case of translating down a rule required for larger bore sizes, with the larger mass of propellant, projectile, and powder, to a smaller size where it isn't needed?
 
Sorry if I am going over old ground for many of you just it seems to me setting off 500 grains of powder would be quite  bit different than 40 and require a much beefier barrel

[Double D]

You are going over old ground. It's good ground to cover, some here have not been over it.

Comparing barrel size between cannons and  small arms can be misleading.  There are two elements in play; scale and a internal balllistics.   I understand them both, I am just not scholarly enough to fully explain them.  You could also say there is a third, element metallurgy.

Yes you can build guns with thinner walls, if you have the technical  knowledge and skill to understand all the issues.  Most, not all guns up to the American civil war  met the wall thickness equals bore diameter rule. As the science progressed the walls got thinner.

If you build to scale one of those designs you should still be safe. 

Because not everyone possess the advanced knowledge or skills, for a general reference here we point to the safety guidelines of the  N-SSA and AAA for construction as minimum standards.  We have sticky at the top of hte board that will point to those organizations websites.

This is for guys like me who just want to build a cannon.

Those with the more advanced skills and knowledge should be able to explain things to you in a  more advance manner.

[GGaskill]

The only part of the bore (or chamber) that needs to follow the 1:1:1 rule is the powder chamber area, and about another bore diameter of length immediately in front of that, say two bore diameters (calibers) total if you are using a straight bore.  At that point you can start tapering the barrel or stepping it down in diameter, depending on what era you are copying, and you will be OK.  The whole barrel doesn't have to be 1:1:1. 

This rule makes for safety even when people use steel of unknown types.  If you were to use a stronger alloy such as 4140, you could go smaller, but then we recommend that you do the engineering design calculations necessary to determine the appropriate dimensions.  "I've shot this for twenty years and it hasn't blown up yet" is not sufficient safety for us to recommend.  The problem with calculations is they depend heavily on the chamber pressure and that is the one thing we do not know with much accuracy.

[jaxenro]

"Comparing barrel size between cannons and small arms can be misleading"
 
Understood, but is a 0.50" (or even 0.75" just slightly larger then a 12 guage) bore with a 12" overall length really a cannon or simply a small arm that resembles a cannon?
 
I'm not stating not to follow the 1:1:1 rule or not to be safe just trying to understand the differences. To me the determining factor in pressure developed would seem to be a combination of bore size, amount of powder, and weight of projectile not the appearance of the piece. A 0.50" smooth bore pistol with 40 grains of powder, a 12" barrel, and a .490 patched ball should develop exactly the same pressure as a 0.50" smooth bore cannon with 40 grains of powder, a 12" barrel, and a .490 patched ball as long as all other factors (chamber shape, etc.) are equal

[Doc Brown.]

Since your on the subject of wall thickness and such. I have a way for you to prove your theories. Purchase the signal cannon bellow. Light the fuse and don't run. Just stand there close by. If you run your walls are to thin. If you stand there your walls are to thick. There can be no in-between with fight or flight.
http://www.ebay.com/itm/SIGNAL-CANNON-INERT-MORTAR-BLACK-REPORT-SALUTE-EMPTY-NOT-FOR-PROJECTILES-NOISE-/221242134008?pt=Vintage_Hunting&hash=item33830f0df8

[jaxenro]

what are those -plastic? Why would I want to shoot off anything so obviously idiotic as that?
 
I have been shooting muzzleloading revolvers, pistols, and rifles off and on for 30 years now and what I was trying to understand is how much of that translates to small scale cannon, those with bore sizes below 1" and mostly below .75"
 
I wasn't aware I had any theories was just asking questions as I am trying to understand what it is that makes it somehow different that it is a "cannon" and not a "pistol"?
 
If you can explain to me why a threaded breech .50 caliber octoganal pistol barrel 15/16" across the flats like this one http://www.trackofthewolf.com/Categories/PartDetail.aspx/628/1/LYMAN-GPP-50-K is safe but the same caliber barrel with a solid breech in steel shooting the same load would require a 1.50" barrel I would appreciate it. Does the barrel somehow "know" it is supposed to be a cannon and the mechanical properties of the steel, gunpowder, and projectile change?
 
However I can easily understand why moving up in scale requires different requirements. A 12 guage shotgun is nominally a .73 bore and was so named because it has 12 balls to the pound. Yet a barrel 12 times the size with an 8.76 bore doesn't shoot a 1 pound ball but so big I wouldn't hazard a guess as to weight.
 
BTW track also sells steel rifled barrel liners in .50 caliber for under $10.00 an inch. Seems like it would be just the ticket for creating a 1:6 scale ordnance rifle from a smoothbore barrel?
 
 

[Doc Brown.]

I sent a very good friend of mine a thunder mug about a year ago. He told me he was going to run some kind of ballistics test and figure out at what point my mug would explode. Never heard from him again. It must take a lot of time to figure out that type of stuff.

[Double D]

 
If you can explain to me why a threaded breech .50 caliber octoganal pistol barrel 15/16" across the flats like this one http://www.trackofthewolf.com/Categories/PartDetail.aspx/628/1/LYMAN-GPP-50-K is safe but the same caliber barrel with a solid breech in steel shooting the same load would require a 1.50" barrel I would appreciate it. Does the barrel somehow "know" it is supposed to be a cannon and the mechanical properties of the steel, gunpowder, and projectile change?
 

For small guns, it is aesthetics, pure and simple. You can build a cannon to BP hand and shoulder arm dimensions and be safe.

Do you want something the looks like a cannon  or do you something that looks like a pistol on wheels.   The cannon you build sends a message---I know what I'm doing or I don't know what I am doing.

There is some advantage gained from the extra weight as the cannon is not hand or shoulder restrained  when fired.  The cannon is in free recoil.  The extra weight helps reduce recoil.

When you get to larger sizes with larger loads then you have to take into consideration the increase in pressure.   

[GGaskill]

If you built a 12 pounder M1857 Napoleon to half inch bore scale, the breech would be 1.2" in diameter.  That is less than 1:1:1, but if you have read the sticky about barrel sizing, we explicitly say that if you build to proven designs, we are comfortable about that.

If you want to build a pistol, then build a pistol.  We would be comfortable about that, too.  But it's really not a subject for this forum.

And ultimately, the amount of powder and shot you load with is going to be a major player in this game and we cannot control that.

[jaxenro]

thanks GGaskill and Double D. I'm not trying to sound argumentative just trying to understand I appreciate both of you taking time to answer
 
What I eventually want is some 1:6 scale civil war cannons, 3" to 12 pounder, which I understand would translate to bore sizes from 0.50" to 0.77". I would like to work as closely to exact scale as I can including bore size
 
I only mentioned black powder pistols because the bore size and barrel length (and load) are very similar and I am familier with safely shooting them and trying to see what limited knowledge of mine is translatable
 
I will probably start with some proven designs like the Scale Artillary models or Brooks and go from there. And I tend to be rather conservative in my loads I don't try to "magnumize" my black powder revolvers either as I usually find accuracy is better with a lighter load