Question on bronze

[One Bullet Dan]

I`ve been toying with the idea of building a half/quarter scale howitzer and was wondering what flavor of bronze would be suitable. I`ve found some reasonably priced aluminum bronze (954) and bearing bronze (932). Any thoughts as to which would be the best for a small scale cannon barrel? Would 360 brass, which is a quite a bit higher in price, be better?

The barrel will be turned and bored from solid round bar stock, if that makes a difference.

Thanks for putting up with yet another newbie question.

[dan610324]

why not collect scrap metal and have it cast ??

[bluelake]

Just keep in mind that there is a difference between bronze and brass.  The former is, chiefly, copper and tin, while the latter often has a fair amount of zinc.  "Gun metal" bronze is about 88% copper, 10% tin and 2% zinc (the zinc is there as an impurity; optimum gun metal bronze would be 90% copper and 10% tin).  Gun metal bronze is relatively strong, but is somewhat hard to machine, while brass is easier to machine, but does not have the strength of bronze.  In other words, for most intents and purposes, a gun should be made from bronze and not brass (unless the latter is just a decoration and not meant to be fired).

If you ever have the inclination to sand cast gun metal, you need to melt the copper first and then add the tin in later, as the melting point of copper (almost 2000 degrees F) is much greater than that of tin (about 450 degrees F); otherwise, the tin would just evaporate.  Also, the price of copper is horrendous. 

[Double D]

We have two resident casters here and they should be able to guide you,

Here is a link to several good post on the subject.

http://www.gboreloaded.com/forums/index.php/topic,205676.0.html
 

[bluelake]

We have two resident casters here and they should be able to guide you,

Here is a link to several good post on the subject.

http://www.gboreloaded.com/forums/index.php/topic,205676.0.html

[GGaskill]

In modern metals practice, any copper alloy containing zinc as the major alloying metal is considered a brass and any copper alloy not containing zinc is considered a bronze.  My castings were made from an alloy called silicon bronze (94% Cu, 6% Si) which contains no tin.  Traditional gun bronze was 90% Cu, 10% Sn which is not a particularly strong alloy.  There are several more complex bronzes that are much stronger than 90-10 tin bronze.

[dan610324]

88-8-4 is one of them

[One Bullet Dan]

We have two resident casters here and they should be able to guide you,

Here is a link to several good post on the subject.

http://www.gboreloaded.com/forums/index.php/topic,205676.0.html

Should have warned me to install my drool guard on my keyboard! Absolutely beautiful!

[Cat Whisperer]

 

[keith44]

We have two resident casters here and they should be able to guide you,

Here is a link to several good post on the subject.

http://www.gboreloaded.com/forums/index.php/topic,205676.0.html

Should have warned me to install my drool guard on my keyboard! Absolutely beautiful!

ditto, those are awesome!

[Soot]

In other words, for most intents and purposes, a gun should be made from bronze and not brass (unless the latter is just a decoration and not meant to be fired).

Board sponsor Brooks USA makes all his guns from 360 brass.
This is the first I've heard of not using brass.

[Double D]

For the smaller  guns  Brooks makes, brass is just fine....but  Gun  bronze is the "correct" metal.

[bluelake]

In other words, for most intents and purposes, a gun should be made from bronze and not brass (unless the latter is just a decoration and not meant to be fired).

Board sponsor Brooks USA makes all his guns from 360 brass.
This is the first I've heard of not using brass.

Hence the qualifier...  As Double D said after:

For the smaller  guns  Brooks makes, brass is just fine....but  Gun  bronze is the "correct" metal.

[dan610324]

is there one correct gun bronze ??  dont think so
many suitable and many not suitable for cannons

if you go back to the 16th and 17th centuries there was as many different alloys used as there where cannons cast .
people knew already back then that a good cannon bronze should be approximately 9 parts copper and 1 part tin
but is the proportions like that in cannons thats been analysed ??   NOOOO 

I guess the bronze is quite forgiving as long as you dont go over 10% tin
a little impurities of both lead and zink is common in all old pieces .
the tin can vary between 2 and 11 %

usually we talk about 90/10 as the classic cannon bronze
US army came up with the modern cannon bronze , 88/8/4
but I dont know when they start to use that alloy

hope someone can help me with a year for that

bells are also cast from bronze , with 10 to 30 % tin
the higher tin content the higher tone in the bells depending on that they get harder with more tin
if you would use a bell alloy with 30% tin for a cannon it would most probably burst on the first shot .

[Soot]

In other words, for most intents and purposes, a gun should be made from bronze and not brass (unless the latter is just a decoration and not meant to be fired).

Board sponsor Brooks USA makes all his guns from 360 brass.
This is the first I've heard of not using brass.

Hence the qualifier...  As Double D said after:

For the smaller  guns  Brooks makes, brass is just fine....but  Gun  bronze is the "correct" metal.

I understand about gun bronze, but where do you make the distinction between small and large guns? At what point is brass unsafe?

[bluelake]

I understand about gun bronze, but where do you make the distinction between small and large guns? At what point is brass unsafe?

First, I would like to clarify that I am nowhere near being an expert on casting/machining cannons like many on here are.  Most of my knowledge is theoretical, as bp firearms are a large portion of my Ph.D. research and dissertation.  However, with that said, you can probably make a "safe" (very relative term there) cannon out of most anything provided there is enough wall and breech thickness for the amount of gas pressure produced by the bp. 

With the discussion on what's bronze and what's brass, here is a bronze that looks more like a brass (source--onlinemetals.com):


Manganese Bronze (C863)
Minimum Properties   Ultimate Tensile Strength, psi   119,000
Yield Strength, psi   66,700
Hardness, Brinell   225
Elongation at break   18%
Machinability   8%
Chemistry   Copper (Cu)   60.0 - 68.0%
Aluminum (Al)   3 - 7.5%
Iron (Fe)   2.0 - 4.0%
Manganese (Mn)   2.50 - 5.0%
Zinc (Zn)   25.0%

[GGaskill]

Safe is a relative term.  One must remember that civil war era bronze guns were considered to have a life of about 500 shots.  Now they weren't quite as heavy as the wall thickness = chamber diameter rule but fairly close (12 pounder Napoleon was 4.62" bore and 11" breech diameter.)  They usually did not fail by bursting but were too inaccurate for further use.  However, we don't know how close to failing by bursting they were.

360 brass is about 58Ksi tensile/45Ksi yield; C46400 Naval Brass is 75Ksi/53Ksi as another example.  Copper alloys also have a lower fatigue plateau than steel, about 35% versus 50%. 

So if you keep records of the number of shots and decommission the barrel at 500, you're probably OK.  But are you really going to do that?

[Soot]

Safe is a relative term, but I would like to understand DD's small gun, large gun, safe for brass, unsafe for brass formula.
Is this based on bore, chamber, gun type?
DD, please explain. 

[Double D]

Safe is a relative term, but I would like to understand DD's small gun, large gun, safe for brass, unsafe for brass formula.
Is this based on bore, chamber, gun type?
DD, please explain.

That sounds more like a challenge than a question.   I put forth no formula, you are pullling that out of your hat, but then you think so am I.
 
Since the only subjective statement I made was small bore I will respond to the that.  I consider under .800 small bore.

You will have to do the engineering your self for a more precise answer. I'm no engineer.  Others here can give you amore precise answer.  George gave you some good numbers to work with and you should be able to use those number to get the answer to your question.
 
 

[Soot]

For the smaller  guns  Brooks makes, brass is just fine....but  Gun  bronze is the "correct" metal.

Since the only subjective statement I made was small bore I will respond to the that.  I consider under .800 small bore.

So, what you are saying here is a gun with a bore over .800 should not be made from 360 brass and would be unsafe?
I just want to make sure that I'm clear because this is a major safety issue, and I've never heard it addressed before.

[Zulu]

Brooks makes an extremely nice 1" bore scale 24 pounder.  It has a 3" breach.
Zulu

[Soot]

I really like that gun and would like to own one someday, but from what I'm understanding, DD doesn't feel that they are safe to shoot.
Brooks also make very nice golf ball bore guns that are quite a bit larger than .800.

[Double D]

So, what you are saying here is a gun with a bore over .800 should not be made from 360 brass and would be unsafe?
I just want to make sure that I'm clear because this is a major safety issue, and I've never heard it addressed before.

I did not say that at all. 

I said do the engineering and get your answer.

[Soot]

George gave you some good numbers to work with and you should be able to use those number to get the answer to your question.

I'm no engineer either and my questions were directed to the statements that you (DD) made.
I'm simply trying to understand what you are saying.

For the smaller  guns  Brooks makes, brass is just fine....but  Gun  bronze is the "correct" metal.

Bluelake considers your statement as the qualifier for his statement about brass guns being just a decoration.

In other words, for most intents and purposes, a gun should be made from bronze and not brass (unless the latter is just a decoration and not meant to be fired).

Board sponsor Brooks USA makes all his guns from 360 brass.
This is the first I've heard of not using brass.

Hence the qualifier...  As Double D said after:

For the smaller  guns  Brooks makes, brass is just fine....but  Gun  bronze is the "correct" metal.

I asked you to clarify your theoretical breaking point between small and large guns, to which you responded,

Since the only subjective statement I made was small bore I will respond to the that.  I consider under .800 small bore.

DD, I thought this was fairly clear but now I confused again. I understand that you are not an engineer and neither am I, but I must conclude that you made these statements based on something but what that something is, has yet to be determined.
If you think my statements are more of a challenge than a question, consider the fact that your conflicting statements are challenging me when I'm simply trying to learn which brass guns are shooters and which ones are decoration. Clarification of your statements could quite possibly save someone life.

[Double D]

1. Determine the working pressures of the caliber you are are going to build. (smaller bores lower pressure, Larger bores higher pressure)
2. Select a material that will contain those pressures.
3. Build the gun to the minimum design standards, including steel liner in material that doesn't have the strength to hold the pressures.

These are the criteria I use to build cannons and to build rifles, it's what they taught me in gunsmith school.

[gulfcoastblackpowder]

The size/material safety issue is really about pressure, as the pressures involved with a large projectile and more powder can be vastly different from those with smaller bores, which use pistol size loads.  There are plenty of historical examples of pistol and blunderbuss barrels being made from brass, which were no doubt considered safe for repeated firing.  Some of these blunderbuss barrels could have quite large bores, but none of them approached most full scale cannon.  I think using information from Parrott-Cannon's VP-Sim program (http://www.gboreloaded.com/forums/index.php/topic,228711) would be a good start in getting numbers, though it is limited in smaller bore sizes.  More relevant numbers would have to be determined through some experimentation, which unfortunately requires resources that most of us don't possess.  I'd personally like to see some pressure tests done on some of these brass pistol/blunderbuss barrels, which would give a good idea of the sort of pressures a cannon in their scale would deal with.

Theory aside, if making your own cannon, why not choose the best materials you have at your disposal?  When safety is concerned, often from an engineering perpective, you size materials that are tested in the given application.  In the case of cannon, there has been extensive testing, and as Dan has said, much of it pointed to what has become known as gun metal, which is a range of alloys around 90/10 that have historically been used with good results.  I know of several cannon made of 660, which is not a particularly strong bronze, but doesn't have a high zinc content, which is the downfall of most brasses (zinc contributes a high brittleness to brass).  There are also many more modern alloys that have also been used successfully (such as silcon bronzes), and are tested in high pressure and peak pressure situations.   These are also viable options, though there is less documentation available in the specific application of cannon, so some more research on the specific alloy may be required, as DD stated.

As far as One Bullet Dan should be concerned, there is no reason to spend more on the 360 brass, since it is known to be inferior for this application.  Some of the bronzes mentioned will have differing machinability, which may be a factor, but I was told when I looked into this a few years ago, that if you're set up for steel, any of them should be easy enough to machine.

[GGaskill]

Some of the bronzes mentioned will have differing machinability, which may be a factor, but I was told when I looked into this a few years ago, that if you're set up for steel, any of them should be easy enough to machine.

That manganese bronze mentioned above had a machinability rating of 8%, but that is comparing it with free machining brass, not steel.  I found when machining silicon bronze that the silicon abraded HSS tooling to the point that it was useless, but carbide tooling worked just fine, even the cheap brazed tools.  Interestingly, I had no problem drilling with HSS drills, only turning with Chinese HSS lathe bits.

[dan610324]

NOW YOU SAID THE MAGIC WORD , CHINESE HSS BITS

try to find some quality HSS and you will see that its possible to use HSS also for bronze

[GGaskill]

The drills were Chinese also, and the lathe bits cut steel just fine.

[bluelake]

Bluelake considers your statement as the qualifier for his statement about brass guns being just a decoration.

Not true.  The qualifier was in my statement (which was in bold):

for most intents and purposes