Bowling Ball Mortar Powder Chamber Design Question...

[OGuthrie]

Greetings Gentlemen,

This is my first post ever here after lurking and reading for about a month. Like many of you perhaps, I was glad for the excuse to shake the neighborhood last night. I have a bronze cannon about 30 inches long, 13/4" bore on a naval carriage. It's a cast of an original 1702 spanish deck gun. Got in a few good blasts last night even though it was about 20 below zero (F) here in Fairbanks, Alaska. ... roll it out on the deck, BOOM...back in to swab and let it rest for a while before reloading...

But, all that is just by way of introduction. I have recently been taken by the obsession to build a bowling ball mortar. I managed to find my way here, and I am so glad to have found these forums! Tons of great information, especially the safety information, and the manufacturers 'reviews'...anyway, I managed (after MUCH labor) to find a cylinder and lopped off the end with a chop saw (many sparks). I was greatly relieved to slide my first ball down the bore and find that it fits!

I don't have much machining capicity on my own, but I have an 'associate' who is a cannon buff and I talked with him and he is ready and willing to help me with the next step. He owns an extensive machine shop, and I'm looking to get started this week.

Here's my first question: Is it necessary to attach a powder chamber, (per the Florida BBM design?) out of say a 5 inch bit of round stock with a 2" X 2.5" chamber bored in it, to the base of the cylinder? Or can one simply remove the valve (already done this) and thread in or weld on some sort of plug, thereby using the natural recess in the bottom of the cylinder for a powder chamber?

I like the blunt looking end without the 5" 'nipple' of the powder chamber attached for aesthetic reasons. But, if it IS necessary, then so be it. It seems like in surfing the web, I've found BBM's built both ways.

After I cross this hurdle, I plan on working on the trunion issue.

My second question is related to 'windage'. The first ball I tried had a nice loose 'rattle' in the bore. Perhaps 1/8" or slightly more space. Another ball, a new one, unbored for fingers, has even less, perhaps 1/32" or less even. That seems a bit tight to me? I'm going to err on the side of caution and I did read the article on windage here on the site, but I guess I'm looking for some field experience here. I plan on using pretty light loads, designed to drop the ball at around 100 yards mostly. What do the 'experts' say?

Thank you gentlemen for your help! I wish you all a happy year and good cannoning!

-Owen Guthrie
Fairbanks, Alaska

[Cat Whisperer]

Owen -

WELCOME to the board!

I think ...  ahhh

I've heard ...  ahh

No.  I'll let those with successful designs comment.

Post some pix of what you shoot!

[GGaskill]

Pressure is primarily a function of powder fineness, powder weight and projectile sectional density. Although a 16 lb ball sounds heavy, its 8.6" diameter gives a lot of surface to push on so the sectional density is a lot lower than a lead or iron shot of the same diameter.  It you limit yourself to 100 yard shots and stick to cannon grade powder, you won't have a problem.  The real problem will be limiting yourself to 100 yard shots.

[Powder keg]

You will love shooting Bowling balls!!! It is a very fun Toy The sound they make in the air is great!!!  I am planing on drilling more holes in one to see if the honking is louder. My mortar is different than most here. It has a pocket in the bottom to centralize the powder. It is also made out of 2" wall pipe. The barrel alone weighs in at near 400 pounds. I built mine before I found this group. Balls very in size. Not only from ball to ball, but when they warm up in the afternoon they are bigger. They also grow (permanently)  if you leave them outside in the sun in your yard. When I built mine I rounded up 10 balls and measured them. I increased the biggest measurement by .030. I figure that if it goes in easy it will come out the same way. If they don't slide in I don't shot them. The heaver balls go farther also. I get my balls from thrift shops, they can be talked down, and yard sales. Also friends and friends of friends.

Wes

[Powder keg]

Forgot one thing. Welcome to the board, you are among friends here.

Wes

[OGuthrie]

Gentlemen,

Many thanks for the warm welcome! I am REALLY excited about getting the beast shooting. I'll try to get a picture of my existing cannon up as well.

It sounds like I'll be 'ok' with the windage I have.

Any final thoughts on whether or not to attach a powder chamber to the bottom of the cylinder?

Again, thanks for the responses!

Sincerely,

Owen Guthrie
Fairbanks, Alaska

[Cat Whisperer]

The powder chamber contains the explosion of the blackpowder during the highest pressure of the burn - not a bad idea to have one, which ever end of the cylinder you use.

[Double D]

Sinch you don't want the Powder chamber sticking out the bottom put it in the inside.

Here is a PS 2.1 drawing showing what I mean.



You are going to need to make the total diameter of the chamber 3 times the diameter of the powder chamber.   You will need a vent liner going from the out side of the tube to the chamber.  I angled the face of the chamber to get the ball a seat.

You can bolt this chamber to the bottom of the cylinder.  Be sure and round the bottom of the chamber so you have no sharp edges to be forced into and through the bottom of the tank and to spread recoil forces.

You could use the bolts to also attach a trunnion bar.

[GGaskill]

If you go with an internal chamber as shown, you should fill the volume surrounding the chamber piece with concrete or something similar so you don't have a large volume for the gas to expand into before pushing on the bowling ball.  It would be a good idea to seal the concrete with something to minimize incursion of powder fouling.

[Cat Whisperer]

Agree with filling the volume, if it's large.  Suggest something less fragile than concrete.

[GGaskill]

I would suggest lead as an easily dealt with material but it will increase the weight significantly.

[OGuthrie]

Thanks, guys, for all the great replies and suggestions.

The internal powder chamber idea was really cool and very innovative. I hand't thought of that at all.

I am a bit worried about trying to get the internal surfaces as clean and smooth as possible. I know myself and I know that I'm not the most dilligent when it comes to cleaning, and I'd hate to worry about corrosion.

I am pretty sure that I'm going to add the external powder chamber as in the original Florida design. It occurred to me that I could use a slightly longer piece of steel and turn a ball or something sort of decorative on the end? Maybe an 8 or 10 inch piece and turn the end into something like a 3 inch dia. knob...? Perhaps that will look dorky as hell. Last night I even thought of mounting the trunions further up the barrell, leaving the barrell a bit longer and making a sort of bowling ball cannon, instead of a mortar...

I just want something simple to build that will be durable as hell, that will, with a big BOOM...send a bowling ball into orbit. But I guess everyone wants that. In the end, I'll probably just go with the straight Florida design.

Thanks again to everyone for your help and responses!

Sincerely,

Owen Guthrie

[GGaskill]

You could make a piece that looks a lot like the M1861 8" siege howitzer.

[Double D]

I wouldn't put any filler in the bottom with the chamber.  It's not needed.  If you do the math you will see the chamber is going be almost as big as the  bottom of th etank.  The ball is going to sit on the chamber.  The space what little there will be is expansion chamber  and will have little effect on anything.

You could  use a large bolt through the trunion bar to draw the chamber down to the bottom and hold everything together.  But I would suspect that might leak gases when fired.

I think I would trim the neck off so the  chamber slipped into the bottom, them weld it in place.  Then I would weld the trunnion bar on.  You need a trunnion on the bottom to have a way to mount the tube in the base and hold it.  A ball on the bottom would get in the way.    Y

Also keep in mind what Bill Tyrell said about the Mortar he built, it like to flip on its back.  You have to have the trunion mounted more center on the base.

As far as corrosion goes,  get the garden hose out and wash the tube out after firing.  Oil and store.

[GGaskill]

Also keep in mind what Bill Tyrell said about the Mortar he built, it like to flip on its back.

The problem with Bill's mortar is the trunnion is mounted too far back on the base, so a straight line through the bore axis passes above the rearmost part of the base which gives the recoil leverage on the base, resulting in overturning.  The bore axis needs to pass through the base, significantly ahead of the rearmost part, for the base to be stable.

[Double D]

Also keep in mind what Bill Tyrell said about the Mortar he built, it like to flip on its back.

The problem with Bill's mortar is the trunnion is mounted too far back on the base, so a straight line through the bore axis passes above the rearmost part of the base which gives the recoil leverage on the base, resulting in overturning.  The bore axis needs to pass through the base, significantly ahead of the rearmost part, for the base to be stable.

That's what I said George, mount the trunion more to the center of the base.