Help Needed - 3/4 Mt. Howitzer Barrel Design

[PATM]

Great forum guys!

I am exploring concept options for a 3/4 howitzer (approx.) build project. I would use 30" x 5" dia. round bar in 1018 or 1045 and bore out the barrel to a length of 24" x 1.70" dia,  leaving 6" more metal for a transition to a reduced dia powder chamber. I am also toying with the concept of drilling and threading a 1" dia breech hole and manufacturing a combination 1" dia breech plug/ 1 1/2" cascabel welded to an additional 5" dia x 3/4"  breech plate. The threaded portion of the breech 1" plug could be approx 3" in length and would extend inside and up to the powder chamber. The purpose of the cascabel/breech plug would be for cleaning out and disarming a FTF.

I have the following questions:

Has anyone else developed this concept and built a cannon with a removable breech plug. I have seen some that are installed and then welded but I wouldn't call that removable.

Are the pressures that would be developed within the chamber during ignition to high for any threaded breech plug design to survive.

What would be an appropriate dimension (dia x length) for the reduced powder chamber design.


Thanks for you help!

Pat M in VA.

 

[KABAR2]

PATM,

Welcome to the forum!

Check this thread it might give you some ideas...

http://www.gboreloaded.com/forums/index.php/topic,215999.0.html

[Double D]

Back in the mid 80's I built 7 or 8 cannons with removable breech plugs. I sold them to others and long lost touch with them, except one.  A couple years ago I had some contact with one of the guys who had one of my cannons.  He told me that he hadn't had the breech plug out in years. The idea was to be able to clean the gun and for  FTF.

I think that the concept is an unnecessary machining step.  

The gun can be fully and adequately cleaned from the muzzle.  As to FTF, one idea about using a vent liner is that it can be removed and the powder flushed and the threads be used as a connector to apply fittings to apply pressure remove the obstruction.  

I think you are way ahead safety wise to minimize the welding and do solid bored gun.

If you don't have them already a good set of plans may I suggest you get them from Antique Ordnance publishers.  

[GGaskill]

The breech ring on a full scale mountain howitzer is 7.6" in diameter so a 3/4 scale one would be 5.7".  If you made your breech plate 5.7" in diameter, you could stay with the 5" diameter with only a little variation from scale.  I'm not sure I would bother with a chamber with a 1.7" bore (golf balls?) 

Pressures are strongly related to weight of shot fired.  If you stick will golf balls, pressures will be relatively low; if you use the Fox steel golf balls, pressures will be higher.  Lead shot would give even higher pressures.  3" of threads should be more than strong enough for the force generated by the propelling gas.

Have you decided what you are going to use as shot?

[PATM]

Gee Guys...Thanks for the responses so far!

You should know that I am not as old as the Howitzer design but I am on the downhill side of 60. (LOL)

I decided to do undertake this project to make it a memorable & bonding experience for my sons (24 & 25 yrs old), not to mention reinforcing the 2nd Amendment we all enjoy. 

This is a concept design so all of you comments are appreciated. I would like to hold close to the 3/4 scale for most of the project with the exception of the interior barrel. Being a working man the cost of using + - one pond of powder per shot is an important factor. That's why I thought a smaller bore dia. 1,70", would be gentler on the pocket $$, while trying to stay close to scale on the OD dimensions.

So if I understand "GGaskill" if I go with a smaller bore then scale, there is no need for a reduced powder area as shown by ButStix ?  Guys your opinions and designs comments are appreciated !!
 
I agree with "Double D" that I am not a great fan of welding on cannon surfaces, there is always a trade off with welding.

The breech plug was only an design option to facilitate cleaning and FTF so I am not locked into that design but thought it was a good idea.The cannon when finished would fire salutes as well as solid shot. I would have preferred a 2 1/8 bore to fire juice cans but that size bore would require a lager OD barrel as well as more $$ per shot.

Knowing the barrel bore is not to scale, is my design strong enough for a powder charge of say 6-8 ozs?

Thanks Guys your great!!!

Pat M in Va


   

[GGaskill]

If you go with a reduced diameter powder chamber, you can still have a larger bore.  My half scale mountain howitzers have a 2 5/32" bore with a 1" chamber and are about 3.15" diameter over the chambers and bronze, not steel.  You could easily go with soda can bore in a 3/4 scale barrel and use a 1.5" chamber. 

Welding on mild steel is not a problem in my mind if well done, although I would not weld 1045.  Trunnions have to be attached some way and I think welding is the best choice as long as it is done by a skilled welder.  I always have TIG'd trunnions (primarily because that is the kind of welding I am most practiced in) and have never had any failures with my trunnions.  In your proposed design, the welding would be attaching essentially decorative pieces to the performing pieces and would not be a concern to me.

[Double D]

There are much better ways to build a cannon than the way bukstix did it and I would not use anything they recommend.   Get the plans from  AOP for a credible reference for your project.  

Take a look at our sticky at the top of the board called Safe Loads and Construction for some basic guidance on cannon construction.  

The most important safety guideline is that the walls over the chamber should be one caliber thick.  You are using  5 inch stock. If the diameter of the barrel over the chamber was 5 inches, the maximum safe diameter of the chamber would be 1.6 inches. You could make a 1.66 howitzer chamber like used on the original gun and have a larger bore.  The section over the Chamber in MT Howitzer would be smaller that forward portion of the barrel.

[Cat Whisperer]

Pat M --

Welcome to the board!  Where in VA?  There are several of us in the Commonwealth.

I'll add two comments, you've got good comments already.

I have a 1/2" bore cannon with a removeable breech plug - it uses a copper disk to crush-seal against a shoulder.  Not sure that it worked well.  I can post pix.

It's my understanding that one looses about half the strength when one cuts threads - lots of places for stress risers.

[GGaskill]

Regarding the concern with dealing with failures to fire, I have had some (bad fuse) in my bowling ball mortar and that will give you pause.  But because the shot is NOT patched, it should roll out of the bore if the bore is tilted downward and the powder will follow with a greater tilt.

The solid breech is much stronger, and if constructed with fillets instead of sharp corners, it will be satisfactorily easy to clean.

Knowing the barrel bore is not to scale, is my design strong enough for a powder charge of say 6-8 ozs?

That is a pretty hefty charge for a small cannon.  The recommended max charge for a 1.5" bore/chamber is only 500 grains (1 1/4 oz.)  6 oz is what I use in my bowling ball mortar.

[PATM]

All this info and guidance is greatly appreciated ! For those who asked, I am located in James City County,Va.
 
I obtained an 1835 Howitzer plan online, it's titled "Artillery from the United States Land Service"....  Source Alfred Mordecai. I would follow this plan for the external barrel contours and scale down the dimensions.

Thanks for the info on the powder charge GGaskill. I feel whole lot better about a smaller powder charge.

The only welding proposed was to attach the trunnions. I thought a 1/4 " bore depth trunnion pocket on each side would be a good idea. Of course, if I scrap the threaded breech plug/cascabel idea, I will still have to attach the cascabel to the back of the breech.

Pat M

[GGaskill]

For a 3/4 scale mountain howitzer, I would make my trunnions/rimbases top hat shaped with the brim .65" thick and recess them such that the innermost edge just reaches the surface of the outside of the barrel.  Doing so will give you a minimum wall thickness of .625" with a soda can bore (2.625") and 1.077" with a golf ball bore.

But you gotta go bigger than golf balls with a 3/4 scale tube.