Dan,
Why the objection to Brass/Bronze? I frequent the European Auction sites frequently (When I have access on the net, like today!) to collect pictures for my library of BP firearms, and I see numerous examples of Naval pieces in Brass or Bronze. There are also several examples that I recall of "Queen Anne" style pistols with brass barrels along with regular flintlocks. Now I admit that this does not preclude that all the other ones ever made didn't blow up in their users faces, but I would think we might have heard more about it.
I looked up the composition of traditional gunmetal, and it is 88% Copper 10% Tin, and 2% Zinc. That's "Copper Alloy No. C90500" Available at : http://www.anchorbronze.com/c90500.htm There's even a Manganese Bronze whose tensile strength specifications exceed that of gunmetal by a factor of two. Of course, 4140 doubles that depending on heat treatment.
Just food for thought and ideas.
I have to figure out how to insert pictures again. It's been so long, that I can't recall how it's done...
Best regards,
Albert “Yes, I am still in Afghanistan!” Rasch
The Rasch Outdoor Chronicles
The Range Reviews: Recreating the 18th Century Powder Horn
Brass work hardens and its REALLY a bad idea for a gun barrel. Bronze was widely used for smaller cannon until the Civil War +-.
Just like steel you need to know the alloy of the material and the quality. When people start discussing making barrels from this or that material and saying they used worse materials in the past I always think of the medical journal article that was reprinted in "The Buckskin Report" of a doctor circa 1840 removing an entire breech plug from a patients eye socket. It had entered at the corner of the eye some 2 years or so previous and the patient finally looked up a physician due to headaches he had suffered since a rifle he was shooting had burst. Not only did the man survive the eye survived removal of the plug as well.
I just see no reason for using anything other than a good steel barrel for a gun barrel. I don't HAVE to use bronze or low quality steel or old wagon tire grade iron so I don't use it. Why would I? I shoot everything I make. Its MY head next to the breech.
Bronze field pieces the Civil War were the only guns without a failure rate, I have read. But this was thought at the time to be the thermal characteristics of the material rather than its ultimate strength. This from a volume on the "Conduct of the War" published by Congress after the War.
So technically the proper Bronze alloy is OK I guess.
When we start thinking of the past we need to understand that failures were common. By the 1860s this was greatly improved as technology improved. But there were still failures. In general these were MATERIAL QUALITY issues. For example I believe nearly 50% of original Colt Walker revolvers failed in service, burst barrels or cylinders. This is why the later Dragoon models had shorter cylinders.
The modern repros made in Italy with gun barrel steel barrels and cylinders are safe with BP. Probably would stand smokeless if it was ignited properly but I would never try it except by shooting the revolver with a LONG string on the trigger from behind a wall or from in a fox hole.
Now does this mean that iron is too weak for BP arms? No it means the iron used was so riddled with inclusions that it was not able to contain the pressures generated. The Civil War US Muskets were ALL skelp welded "best" iron and they STILL have a good safety record. Though shooting one regularly is silly IMO.
Since I have no idea what the quality rating is of a bar of Bronze bought from some supplier is I don't know if its safe to shoot. I suspect there are different levels of quality in copper alloys too since the are used in applications like power plants and perhaps nuclear submarines.
The thing is that BP produces such low pressure compared to the strength of the material that it should be impossible to burst a steel barrel EVEN WITH A BARREL OBSTRUCTION. Yet barrels fail. So this tells us that the material is at fault. I cannot in good conscience have someone make a barrel from questionable material without at LEAST pointing out that it might not be safe.
BTW if the material is not suitable for the application no proof load or other "test" will assure it will not fail in use.
If people choose to make Bronze barrels or barrels from PVC pipe its THEIR affair. But they need to be able to make INFORMED decisions.
BTW the TENSILE numbers of a material does not necessarily translate into its ability to contain pressure.
Dan