Brass versus bronze

[Frank46]

Just received the monthly Enco flyer. I noticed that the prices for brass alloy 360 3" in diameter per foot $254.32 versus sae 660 3" is
$136.49 and the 3.5" is $177.83 for 13" lengths. Is either alloy suitable for making a firing cannon or mortar?. I'm not a metallergist by any means, but I'm guessing that the bronze would be the stronger of the two metals.. By the way Tropico your swivel guns are truly works of art. Regards, Frank

[Tropico]

Probably I would take the bronze for a larger cannon. GGaskil is our local metallurgist , I would take his decision and use it.
How large a bore will you be making with the stock., whatever the bore or model cannon ., I would take the 3.5" stock. its not much more money and the 1/2" is substantially more noticeable.

[Frank46]

Tropico, well I already have some 3" alloy 360 brass extruded rod,but the bronze I believe is the stronger of the two. At 13" long allowing for cleanup of the ends Should come out about 12 3/4" long. But here is the rub. I have no idea on how to attach the trunions. I'm assuming that they are brazed or silver soldered on. I have no brazing equipment and do not know anyone locally who I would trust to do the job.At this point it would be better to have someone who is very familiar with the technology to do all the work. Was thinking something like a 24 pounder. With a 1" bore that occasionally I could fire some lead balls. Lead I have plenty of. With that said the bronze at 3.5 inches would be the most one suited for what I have in mind.Thanks for your response

[GGaskill]

...GGaskil is our local metallurgist

I would have to take exception to that statement.  :-)  Metallurgical conscience, maybe.  You could make a safe cannon from either material, as long as you don't make design errors and loading errors.  It's how much powder and what kind of shot weight as well as what materials and what dimensions that determine a safe gun. 

The forum rule of thumb is wall thickness equals bore diameter (in a chambered piece, the chamber diameter is used, not the bore for the shot.)  So you could probably make a 1" chamber/1.5" bore  mountain howitzer from 3" brass or bronze, but a 13" length would be proportionately short by about 2".  Although it would be nice to be able to shoot golf balls, the barrel walls seem too thin for me unless you use some other design.

Check the Anchor Bronze website for material specs.  360 and 660 are older specs.  660 is now 93200 but I don't know what 360 is.  You can probably find it on the Anchor Bronze site if you look hard enough.

[Tropico]

Oddly enough I happen to have a 3" diameter X 12" length.,  1" bore 24 pounder. Also it is 360 brass. It is very strong and is one of my treasured guns. It was made by    http://brooks-usa.com/_wsn/page9.html Brooks USA .
It makes a Big Bang., toss's a 3oz lead ball like a boolit ! And looks awesome in the living room on my lamp table next to my favorite easy chair.   If you contact Michael at Brooks USA ., I bet  he would be happy to make you a cannon .

[Frank46]

George, checked the anchor site you suggested and they list c36000 free machining brass, no 93200. This is still in the planning stage as I have a few projects I have to get done before I even think about the cannon. I value your opinion, thanks,Frank

Tropico, yep that sure is a little beauty. kinda like the mortar in your pics also. Frank

[GGaskill]

C93200

 -or-

C93200 (SAE 660) Specs


C36000 Specs

Comparing these two alloys, the brass is substantially stronger than the bronze, but look at other bronze alloys for greater strength.

[Cat Whisperer]

C93200
...
C93200 (SAE 660) Specs
C36000 Specs
Comparing these two alloys, the brass is substantially stronger than the bronze, but look at other bronze alloys for greater strength.

Good references.

One thing that MUST be considered is how the metal reacts to repeated stresses of firng.  This is not in the charts because most folks buying these materials don't build cannons.  Further, most folks building cannons don't use brass or bronze but modern materials.

The issue, again, is cold working.  Neither brass nor bronze are good materials.  (Hence, when steel was figured out it revolutionized the making of cannons - by using 'mild' steel - new in the 1870's.)

That brings us back to the original question of safety. 

I have found but ONE metalurgist ever who comments on these boards on the strength of materials such as these for making cannons.  His conclusions were much the same as what we've come to - avoid the leaded steels (which are very 'strong' and GREAT for machining but tend to develop brittleness with working - take a look at the Charpy Notch test results).  But we're talking about brass/bronze.

Follow the EXPERIENCE of successful designs.  FOLLOW the RULES of design of those organizations, that have been successful for YEARS, that have recommended items included in the following list.  Read SWITLICK's: The More Complete Cannoneer and other good references.

• Minimum wall thickness ALL around POWDER CHAMBER equal to the diameter at that point
• Round the inside corners (or do a spherical bottom of the powder chamber)
• Longer powder chambers devlop higher pressures than shorter ones
• prudent loading (powder type and quanitity and NO patching [with some minor exceptions]) must be observed
• Windage (clearance around the projo) reduces pressures, hence is safer, and accomodates irregularities in projo diameters

[Double D]

The one caliber minimum wall thickness rule of thumb is not a board rule o thumb but a rule  imposed on  Cannon used in N-SSA competition.

[Frank46]

I have to agree with what has been said about leaded steels, they finish well, but are prone to rupturing. Think that there was some articles done in a blackpowder magazine about using these steels for barrels and that some had ruptured and caused injuries. I am somewhat familiar with the charpy notch test. In a liquified natural gas tank, we had coupons that were removed on a scheduled basis and that test was used to determine wether or not the tank had reached the end of its service life, minus 240 degrees below zero.
But the subject is still about safety. Will get Matt Switlik's book and whatever orther info about this subject. Thanks to all. Regards Frank

[cannonmn]

The brass/bronze parameter comparison above used "bearing bronze" which is a good bit different from the old, nominal  90/10 gunmetal bronze.  As long as we're looking at that particular site, look at their phosphor bronze which is closer to gunmetal in composition.  The tensile and yield strengths shown are close to what I'd expect for gunmetal.

http://www.anchorbronze.com/c51000.htm

[GGaskill]

C90700 is very close to 90/10 tin bronze.  It is not a particularly strong or hard metal, although it has the history of being used as gunmetal in the past.  Modern "gunmetal" is a more complex alloy and there are many alloys that go by that name.  This book is a good reference about casting modern gunmetals.

[Cat Whisperer]

Not particularly strong is overcome by good design and proper loading.

Not hard - is good!  That also says is not brittle (well sort of).  To hard and brittleness is right there biting at your heels.

[cannonmn]

Just to add another complicating factor into the equation, thermal conductivity probably has a role in cannon endurance, particularly where the vent is involved.  Hobby cannon shooters probably don't have to sweat this much since it is easy to tell when your vent is too worn, so you can rebouch it.  In the old days, a bronze gun might be a few countries away from the arsenal when it got into some serious action, and it had to fire a lot of rounds in a relatively short period of time.  The users did not want the vent to wear out while they were still trying to breach the castle walls or whatever.

Bronze of roughly 90/10 was used as the primary field cannon metal for hundreds of years, up through the US Civil War at least, and I have to think it was arrived at as a result of a whole lot of trial and error.  But again, it was the obvious choice for tactical weapons which had to be safe and have a lot of endurance, and the second factor doesn't really apply that much to small hobby cannons.

Any comments from the staff metallurgist are most welcome.