Howitser Idea/Questions

[NitroSteel]

I have a 16" long piece of 4" ID/ 6" OD steel stock that I was thinking of making a howitser out of.  My idea was to insert a 5" long piece of 4" round stock into the rear with a 2"x2" chamber.  Chamfer the outer rear portion of the 4" round stock, and the inner rear portion of the 4" ID stock and weld the pieces together.  The pieces will fit together very tightly, but they will not be sweated together.  We've used the same type setup in making some softball/propane cylinder mortars and haven't worried about them at all - since the trunnion keeps anything from seperating (the force actually holds it all together for the mortar), but of course on a howitser the trunnion is not mounted along the rear, but on the sides.

My question is:  is this a strong enough way to put these together?  I don't want the pieces to seperate and hence shoot the 5" long piece of roundstock rearward instead of the projectile forward...  I can't imagine that this would ever happen, but I wanted to see what ya'll thought.  I'd thought of also boring a 1" hole through the apparatus and "pinning" them together with a piece of 1" diameter round stock (and still welding all the pieces together).

Assuming the above is acceptable, I have scaled up some barrel plans that were posted here by dan610324 on another post (http://www.gboreloaded.com/forums/index.php/topic,178567.0.html).  The scale will be perfect for the barrel proportions, but I'm not sure what size the carriage should be.  How big was the outer diameter of a full size mountain howitser's barrel at the breech, and what was the diameter of the wheels?  Better yet, given that the above are my planned dimensions, how big should my wheels be (from the looks of things, I can use the same plans that I used for my Parrot Field Rifle and just "resize" them to make it proportionate to my barrel).

Thank ya'll for your help.  I know this is alot to ask on one post, but I'd rather ask before I get started.  On my golfball cannon I wish I'd asked more questions about the breech design before I started (it is threaded for easy removal), I don't want to have any regrets on this one.

NitroSteel

[Double D]

I'm pretty sure I grasp what you are going for.  I suggest you take a look at the N-SSA rules on the construction of breech plugs. 

You need some way to seal the breech plug tightly so powder fouling isn't forced via pressure and condensation between the wall of the breech plug and barrel.  There are several ways to do it and shrinking is one of the best.

There is no comparison of the dynamics of a propane cannon and black powder cannon.  Do it wrong and you have bomb waiting to explode, and it may take years to fail.

[NitroSteel]

Gotcha Double D, I'll read up on the link.  But, when I mention propane cylinder mortars, I'm talking about the projectile being a propane cylinder - the propellant IS blackpowder on all of the above.

Thank you,

NitroSteel

[GGaskill]

I'm thinking it would be better to thread the breech plug into the barrel instead of welding it so you can take the pieces apart for thorough cleaning.  If you weld the pieces at the rear, you will have a gap in the front that will collect fouling and be impossible to clean.  At least a screw breech can be taken apart and completely cleaned.

[NitroSteel]

My golf ball cannon breech plug is threaded and I was told that eventually the threads will "roll" off and the plug will be blown out if I shoot heavy projectiles with it.  Now I'm always nervous when I shoot it (so I pretty much don't unless it just has golf balls or blanks in it).

How is the strength on the threaded breech plug, versus one that is welded?

NitroSteel

[GGaskill]

My "Parrott" rifle has a threaded breech and I have no fear that the threads will catastrophically fail.  But I also inspect them when it is unscrewed for cleaning.  Don't use a really fine pitch thread and you should be OK.

The welded-at-the-rear breech with gap at the front has both the corrosion issue and a trapped sparks issue as the corrosion gets worse.

[NitroSteel]

Is 12 tpi o.k. (if not what is)?  How deep should the treads be (minimum)?

Thank you,

NitroSteel

[GGaskill]

I would say 2" of 12 tpi would be fine.  Mine is 2" of 16 tpi, which takes a long time to unscrew. 

Now having said that, I must say I am not an engineer and have done no math to prove that.

[dan610324]

just a welded plug without the shrink fitting with a large (deep) chamfer to weld in is in my opinion a very dangerous construction, you will only have that little weld who should hold all together

why not try to find a solid bar at the scrapyard instead ??

[KABAR2]

If properly constructed a threaded breech screw should be fine,

they have been used for hundreds of years in muzzle loading rifles & muskets and you rarely hear of a failure in those,

if you did it would most likely be some bubba used smokeless powder instead of BP. 

The breech on a musket is rarely removed for cleaning  I will tell you this I have worked on and restored about a hundred muskets and rifles over the years,

most of them if I removed the breech plug it was probably the first time it had ever been done in the life of the gun,

 I rarely found rust or corrosion in the threads past the first thread and these are on guns 150 to 200 years old.

the problem comes from removing the breech all the time that is when you get thread wear, the more you screw and unscrew it the more it wears.

that being said there is nothing wrong with a shrunken and welded breech, and as had been said the press fit and welded are the ones with the issues.