barrel safety? first post

[handelshannon2]

Carpenter by trade but always interested in cannon I started out by building a prairie carriage.Last year I purchased a hern iron works mountain howitzer barrel. It has a 3" bore with a 1/2" seamless liner and a radiused and welded breach plug.  I installed a brass vent .I have been casting 2.925" zinc balls as a projectile. The powder charge I have been using is 7 oz cannon grade wrapped in foil. After learning about this site and researching I see that my barrel doesnt meet min. construction standards(chamber thickness).Is this barrel safe to fire? Thanks

[GGaskill]

The current policy is that models of professionally designed guns are OK if the same proportions are used.  In this case, we are taking a bronze gun and reproducing it in cast iron with a steel liner.  The cast iron is more brittle than bronze, but the steel liner somewhat makes up for that.  The chamber of a real one is 3.34" diameter, a little larger than your chamber area. 

Personally, I would lower your charge from 7 oz to 6 oz (2 oz per inch) and proceed.  But you should inspect the inside of the barrel after cleaning it after every firing session just to be sure.

[Zulu]

Does the mountain howitzer have a powder chamber?
Zulu

[handelshannon2]

Barrel is straight bored no powder chamber, maybe 1 3/4 wall thickness at chamber.
 

[GGaskill]

Original drawings show diameter of the chamber is 6.30".  Assuming the repro is the same, the wall thickness would calculate as 6.30-3=3.30, 3.30/2=1.65".  .5" of steel, 1.15" of cast iron.

[handelshannon2]

Thats pretty close, I measured with a tape measure. Still no where near 3".

[GGaskill]

Still no where near 3".

That's true and most of it is cast iron which is not strong in tension.  If I were committed to this barrel, I think I would add another steel sleeve inside the existing one.  It would add more steel and reduce the bore diameter, both of which would lessen the stress on the cast iron.

[clum sum]

If it is a Hern tube check for bulges and if the liner is stright with the outside of the barrel. Thought I was geting a concave breech but got a flat one. Wish You luck.

[handelshannon2]

I am very happy with hern,It does have a radiused breach plug.When I had A friend true up the trunions he indicated the bore and in was perfectly in line with the outside. I bought a pendullum rear sight and installed a front sight. The cannon shoots great. Could I reduce just the chamber area diameter with a sleeve and not the whole bore? What about corrrosion between the two? Or could I just reduce powder charge and run it like it is?