Editor’s Note: This cannon safety article was first printed in the Winter 1984 issue. Thanks to Paul Barnett of South Bend Replicas for providing the photos.
Since the revival of active use of Muzzleloading artillery in the 1950s, the economics of casting reproduction gun tubes around steel tubes of various kinds has encouraged a large number of makers to utilize this basic technique.
Shortly after I began planning my first reproduction cannon in 1959, I found an article in Guns magazine which described the casting of a reproduction bronze gun around a steel liner.
Following information in that article I completed my first cannon in 1961 by having it cast at a local foundry. Within the first day of owning my cast iron 2.6-inch smoothbore replica, I became alert to potential problems with guns cast in this manner.
My liner was quite heavy, about 5/16-inch wall thickness, total casting about 220 pounds, bore was about 38 inches deep and the liner was well-secured at the chamber and muzzle and had been well packed with core sand during casting.
Although the bore remained smooth and uniform in diameter throughout its length, after casting it had a uniform bend with about 1/2-inch displacement at the mid-point of the bore. Accuracy was disappointing to me and within two years the gun was spiked and sold to an interior decorator.
In the following years I have had the chance to visually inspect many different pipe-cored guns and have noted a wide variety of distortions in varying degree which resulted from the casting.
These have included scabs where iron burned through thin-walled steel tubes, globs of iron which leaked into chambers, partial collapse of tubes, off center and bent bores, and exterior chill fractures when a thick-walled 75mm tube was used in one case.
It was not until this year that I had the chance to do any "destructive” inspections on guns, by actually having them cut apart.
The results of the first two such inspections were reported in the Summer 1984 issue of The Muzzleloading Artilleryman. The interior condition of the small pipe-cored gun in that article pointed to the need for further study.
I had been surprised at the extent of shrinkage of the steel away from the iron at the breech. Cannon of this type have often been described as having liners "permanently fused" to the iron casting. The first such gun which was cut apart did not show any kind of bond between the iron and the steel, other than the mechanical interference caused by liner warpage and distortion.
Since the pipe-cored gun studied above was relatively small, about 1-inch bore, I felt at the time that study of a more typical field gun reproduction would be interesting.
The opportunity to view another dissection came up this fall and the results are illustrated here. The gun is about a 3/4-scale of the M1841 6 pdr. cast in iron with a bore of 2-3/4 inches and a liner wall thickness of 1/4 inch.
Again, dramatic shrinkage has occurred. After the breech was cut off, the liner section in the chamber fell out. The airspace behind the liner had been about 1/4 inch as seen by the fact that the liner section slid back that far when reinserted.
Even more interesting was the fact that the steel plate of 1/4-inch thickness had domed inward, apparently from the extreme heat, creating a chamber configuration with sharply recessed corners, quite the opposite of traditional chamber design.
The cast iron which solidified against the breech plate was flat. As the steel cooled it pulled away from the cast iron and the breech plate domed into the bore almost 3/8 inch.
Several other cuts were taken on the tube and in all cases the liner separated easily from the cast iron. A chaplet was also not fused to the casting.
In conjunction with the situation in the chamber area, the possibility of the failure of the breech plate weld seems quite likely. Also, the possibility of the liner setting back against the iron breech, thus obstructing the vent during firing, seems plausible.
If by chance neither of these situations developed with a particular gun tube, the convex breech face would tend to resist clean sponging and would allow the accumulation of carbon and other residue.
The effect of vibrations promoted by the loose fit, at least at some points between the iron and steel, is open to speculation.
Persons having guns cast on the pipe-cored system should be aware of the possibility of these conditions existing.