New to the forum, a few questions

[airco02]

Finally found a place to get info. Hello from Canada
We are currently looking to turn a 1/3 napoleon from 4140 steel
Safety is our main concern, The bore will be 1 11/16 for golf balls
breech 4" muzzle 3.5, this leaves ..90 barrel thickness, less .25 for the narrowest part of the barrel (where it dishes in before the muzzle swell)
leaving .40 per side of barrel thickness. Is this adequate?
 I have read somewhere that golf balls can be dangerous to use do to them compressing upon firing, is this true?
Thanks, Have a few more question re: trunnions etc. to ask later.

[Double D]

You will find your best answer here:

http://www.n-ssa.org/NATIONAL/RULES/section21.html

Actual or exact scale replicas of Civil War artillery pieces may be fired. The term "Civil War" applies to any artillery piece whose model antedates April 26, 1865. Except for mortars (whose separate regulations are covered under Section 22), replicas of artillery pieces must have a barrel length of at least 40 inches, a bore diameter not less than 2 inches, and a wheel height of not less than 36 inches. All reproduction barrels must be made of iron, steel or bronze. All reproduction barrels and those original barrels failing inspection, must be lined with a bore liner of extruded seamless steel tubing of a minimum ANSI standard and of a minimum 3/8-inch wall thickness. The liner must be closed at the breech end with a steel plug, sweat-fitted into the liner and welded. The breech plug must have a radius of at least 25 percent of the bore radius and be at least 1 inch thick at its thinnest point. (See figure 21.1.) All reproduction barrels manufactured after March 1, 1986 must have pictures of the liner and breech plug before and after welding. No reproduction barrel shall be approved after March 1, 1986, which does not have one caliber's thickness of metal surrounding the bore at the breech. (See figure 21.2 for example.) Liner may be affixed by casting barrel around the liner or by other approved methods such as bonding with high strength adhesives. Method of locking liner in barrel shall be approved by the Artillery Ordnance Officer. The gun and its crew must pass the inspection specified in Section 21. No person shall be permitted to serve as a member of a gun crew unless he is a member of the organization to which the crew belongs or is a member of another registered crew. A gun crew shall consist of a minimum of 4 members of the organization. Effective 1 February 1996, all artillery pieces must be originals or full-size, exact replicas to be approved. (February 1996)

These are the rules for the North-South Skirmish Association.  These fellows have a great deal  of knolwedge and experience and would trust their wisdom.

Your golf ball size gun would need to be 5 1/16 inch  in diameter over the chamber to meet the NSSA safety standards.  The muzzle diameter can be smaller. given the liner can be no thinner  than  3/8 then I would think that would apply to to the smallest diameter on a steel barrel.

You do have a extra margin of safety using 4140.

[airco02]

Thanks for the link. It looks as though I will have to go to a larger scale
to achieve the correct thickness, thats a bummer because a already started the wheels and have laminated two felloes at 19" (1/3 of 57).
 I choose the barrel thickness base on info I found on the net, I wll try to find it again and let you know which site.

[airco02]

hello D.D.     The site that I found the 4" barrel www.brasswithclass.com
They show two civil war replica cannons with 4" breach. I felt that a manufacter would know what he was doing and so was planning to use his specs. but will rethink things now.
Best regards

[Double D]

Just because you can build something doesn't mean you understand how to build something.

Understand that NSSA has rules to make cannon shooting safe to fit there sport.  They make the rules for full size guns and from prior experience.    If you notice the rules say one caliber thickness over the breech for brass, cast and steel. Steel is a lot stronger than the other two.   It would be difficult to enforce one rule for bronze and cast and another for steel, so they have one rule.

For additional guidance you can look to Roy Dunlap's book on Gunsmithing.  Dunlap stated that the cylinder wall of a high pressure rifle barrel should not be less than 2/3 as thick as the diameter of the cartridge.  This is the generally accepted rule for Smokeless powder rifles

Since the gun tube you are considering is made from 4140 "Ordnance" steel, I think you could apply Dunlaps rule. Your chamber is  1 11/16.  2/3 of 1 11/16 is .5623.  1 11/16 plus .5623 plus .5623 is 3.9368 according to my on line calculator.  

Get your cannon and shoot black powder.

[Trigger Mortise]

If I read your calculation correctly, the narrow part of the barrel is 3” and the walls in that area are .650”.
A diameter of 3.375” and a wall thickness of .837” in that area would be adequate for mild steel with a tensile strength of about 70000.
Your 4140 has a tensile strength of about 90000, going by that, I would say that you’re ok with this.
Welding 4140 requires a little know-how, so do your homework.

[airco02]

Thanks Gents, I have 30yrs experience with cartridge rifles both black powder and smokeless , use to have Dunlops book,lost it and many of my pieces I a fire sometime back, Hence the questions. I prefer to err on the side of safety.