Guide for Building a Bowling Ball Mortar.

[DH2]

Hello All!

Recently, for a class that I'm taking, I wrote an Instruction Manual on how to construct a BBM based off a 10" seacoast mortar from the 1860s. Following this initial post is essentially a series of copy pastes of that instruction manual as well as the drawings I had to create for it. Id very much like your suggestions and critiques.

Just a few notes though:

I only put critical dimensions down on the drawings (mainly the ones for the carriage). This allows for personalization/customization.

The size of the powder chamber in the breech plug is supposed to hold 2oz or less of powder (going off of someone's post saying their chamber of Volume X held a Weight Y of Goex) from what I've seen on this forum and others, this should wind up with a max range somewhere in the 2-300 yard rage at 45 deg. I figured this was long enough for beginners.

The next iteration of drawings will include a thread call out for the touch hole to allow a Percussion cap nipple to be screwed in, as well as drawings for a slap hammer and mount. I ran out of time for the paper or these would be included on this iteration.

Thanks in advance!
DH2


One other note: I'll be building a mortar along these lines as the time and funding allows. I'll catalog the process in another thread.

NB: Edits are in red.

[DH2]

Introduction:

   Congratulations, you have decided to join the ranks of amateur artillerists everywhere and construct a Bowling Ball Mortar. Before you begin however, there are some cold hard facts that have to be presented in a rather stark and serious light. Building and firing black powder artillery is a dangerous hobby. Even if you do everything right, things can still go wrong, and when you are dealing with black powder, large weights, and metal, the results are not often pretty. In this guide, there are numerous tips, hints, and outright warnings that need to be followed to help you enjoy your Bowling Ball Mortar in as much safety as is possible. Despite the risk inherent in building and operating black powder artillery, it can still be a very fun and exhilarating activity. The 4th of July will never be the same again once you’ve sent a 16 lb bowling ball whistling through the air and into the distance. Nothing makes a bigger boom, nothing gives you as an exhilarating rush, nothing is as much fun, as the roar of a cannon and knowing that you made its existence come about.




Using This Guide:

   This guide contains instructions, hints, tips, and warnings that are essential for the safe and fun operation of your Bowling Ball Mortar. It should be noted however that the instructions in this guide do not represent the only ‘right’ way to make a Bowling Ball Mortar, nor are the tips and warnings for safe operation comprehensive. Like any risky activity, a great deal of common sense will help you head off mishap.

   One thing you will immediately notice about the instructions in this book is that there is no list of tools required to complete a particular step. This is done intentionally. Some of the steps in this guide require specialized tools to complete. These specialized tools require specialized skills. If you do not have these tools or these skills, then it would be a very good idea for you to find someone that does and ask them for help before beginning this project.

[DH2]

Legal:
   
   The Bureau of Alcohol, Tobacco, Firearms, and Explosives, referred to here as the ATF, is the government agency that writes regulations to control things like your Bowling Ball Mortar. Fortunately for us and for amateur artillerists everywhere, there is a specific exemption in the ATF’s rulings that allows us to build your Bowling Ball Mortar without fear of legal troubles. According to their rule, which is posted below, your Bowling Ball Mortar is considered to be  a replica, and is therefore not something that carries any special rules or regulations on a federal level. Below is the relevant excerpt from federal laws that fairly clearly (comparatively speaking) explains that your Bowling Ball Mortar is in fact a benign replica:

26 USC sec. 5845(g) "Antique firearm.-The term 'antique
     firearm' means any firearm not designed or redesigned for
     using rim fire or conventional center fire  ignition with
     fixed ammunition and manufactured in or before 1898
     (including any matchlock, flintlock, percussion cap, or
     similar type of ignition system or replicas thereof, whether
     actually manufactured before or after the year 1898) and
     also any firearm using fixed  ammunition manufactured in or
     before 1898, for which ammunition is no longer manufactured
     in the United States and is not readily available in the
     ordinary channels of commercial trade."


   Because your Bowling Ball Mortar is loaded with the propellant separate from the projectile, uses simple cannon fuse for ignition, and is patterned off of a Seacoast Mortar in use in the 1860s, it is falls clearly under the federal definition of a replica firearm.



Even though your Bowling Ball Mortar falls under the federal definition of a replica firearm, the laws of your state, county, or municipality may be different than federal law and have more stringent rules. It is up to YOU to know what laws dictate the construction, possession, and operation of your Bowling Ball Mortar in your area.

[DH2]

Safety Briefing:

   During the construction of your Bowling Ball Mortar, there are several safety tips to consider during the entire process. More specific safety tips will be provided where necessary, but below of some general safety guidelines to follow throughout the construction process:

1)   When using tools to shape, form, modify, or in any way ‘mess with’ metal, safety goggles are a must. Wearing safety goggles will help you to preserve and protect your eyesight in the event that chips separate from your work piece and fly towards your face.

2)   When cutting metal, the resulting chips and edges of your work piece can be quite sharp. It is recommended that you refrain from touching these edges or chips with your bare hands. Wearing gloves to move your work piece and using a shop-vac to clean up chips will prevent nasty cuts on your hands as you progress through construction.

3)   If you do not know how to complete a construction step, it is advised to recruit a Machinist or Certified Welder to help you complete the step. This will help to keep you safe during construction, as well as ensure that your Bowling Ball Mortar will be as safe to use as possible.   

[DH2]

Section 1: Materials

   In order to construct your Bowling Ball Mortar, you will first need to acquire the proper materials to do so. The list that is provided below aims to direct you to the most appropriate materials at the least cost while not sacrificing anything by way of strength or safety.

Mortar Materials:

•   K Sized Gas Cylinder. These are also identified by their Department of Transportation designation of  3AA2400. This type of cylinder is the ONLY type that will work and is what you must use for the barrel of your Bowling Ball Mortar. These gas cylinders are the type used by welding shops everywhere to hold pressurized gasses. Empty ones can be found at welding shops and at junk yards for reasonable prices. Before purchasing, make sure that the tank is EMPTY.

•   A 6” diameter piece of solid round stock at least 4.5” long made of either 1018 or 1024 mild steel. This will be used to form the breech plug and powder chamber of your Bowling Ball Mortar.

•   At least 12” of 2” diameter steel bar stock. This will be used to create the trunnions of the Bowling Ball Mortar.

Carriage Materials:

•   4x 2”x12”x36” Lumber, preferably oak

•   4x 4”x4”x8” Lumber, preferably oak

•   10x .5”x14” Carriage Bolts

•   1x .5x 8” Fully Threaded Carriage Bolt

•   11x .5” Nuts that fit on above Carriage Bolts

•   Wood Glue

Mortar Sponges:

•   2x .5” x 36” Wooden Dowels.
 
•   8x Old Socks

•   2x Zip Ties

[DH2]

Section 2: Construction

Following this section are engineering drawings to provide a reference to how to construct and assemble your Bowling Ball Mortar.   

Step 0: Open all valves on gas cylinder and leave it outside for AT LEAST 24 hours to ensure that the cylinder is EMPTY.

Step 1: Clean any rust or paint off of the Gas Cylinder.

Step 2: Cut off the top of the gas cylinder to remove the gas stem. The result of this cut should be that there is an approximately 6”  diameter flat plane on the top of the gas cylinder.

Step 3: Using the new top of the cylinder as your measuring point, cut the Gas Cylinder down to a length of 18.” This length of cylinder will be your barrel. Ensure that your barrel length does not exceed 18" as this will adversely effect the function and stability of your Bowling Ball Mortar.

Step 4: Bore  a 2” diameter hole into one end of the breech plug to make the powder chamber. This hole should be bored to a depth of 2” This is the chamber that will hold the powder and direct it's expanding gasses to propel the bowling ball. WARNING: DO NOT MAKE THE POWDER CHAMBER ANY DEEPER OR WIDER THAN 2" AS THIS WILL RESULT IN A WEAKENED AND UNSAFE BREECH PLUG.

Step 5: Weld the breech plug onto the 6” diameter plane on the top of the cylinder. Be sure to position the breech plug with mouth of the powder chamber facing the barrel. This step should be completed by a certified welder.

Step 6: Mill a flat into the bar stock. This flat should be 6” across, 1” deep, and be positioned in the middle of the bar stock. This will create the trunnions that will keep the Bowling Ball Mortar attached to the carriage as well as provide the pivot point for elevation change.
   
Step 7: Weld the trunnions onto the back of the breech plug. This step should be completed by a certified welder.

Step 8: Drill a 0.2” hole 3” into the breech plug so that it pierces the side of the chamber. This hole should be positioned perpendicular to the trunnions. See Breech Plug drawing for positioning details.

Step 9: Cut out 2”x12” lumber following the contour shown in the Carriage Pre Assembly Drawing.

Step 10: Glue 2”x12” cut outs together in pairs.

Step 11: Assemble Carriage according to the Carriage Assembly Drawing.

Step 12: Put 4x socks on one end of each dowel, Zip Tie in place.

Step 13: Paint your mortar and carriage as desired. This is an optional step, however, painting your mortar and carriage will help to  preserve them and protect them from the elements.

[DH2]

Firing Your Mortar:

Legal:
   
   Operating your Bowling Ball Mortar Safely and Legally is YOUR responsibility. You must research your state, county, and municipal laws to ensure that you can legally fire your Bowling Ball Mortar in the area. If you are firing your Bowling Ball Mortar on Private Property, the you MUST obtain WRITTEN permission to use the land for that purpose.  

Safety Brief:

   Firing your Bowling Ball Mortar takes a great deal of common sense as well as a great deal of caution. You will be dealing with very flammable black powder; as well as heavy weights moving at a great deal of speed. Therefore, here are some safety guidelines that you should always follow:

•   At all times ensure that no one is in front of the Firing Line unless the Bowling Ball Mortar is disabled.
•   Always wear eye and ear protection while firing the Bowling Ball Mortar
•   Always keep your Black Powder in a locked, non metallic container.
•   ONLY USE BLACK POWDER!!! Standard gun powder WILL cause your Bowling Ball Mortar to EXPLODE.
•   Always sponge out the Bowling Ball Mortar between shots to extinguish and clean out any powder residue.
•   Always use a powder measure when loading Black Powder into the Bowling Ball Mortar, using the original container can result in a dangerous explosion.
•   Ensure that no one leaves the Safety Area until the Bowling Ball has come to a full and complete stop.
•   Never fire the Bowling Ball Mortar if you cannot follow the entire flight of the Bowling Ball.

[DH2]

Step 1: Obtain the following materials:
   Any Number of 14-16# Bowling Balls
   FG or Cannon Grade Black Powder (MUST BE BLACK POWDER)
   A Locking, Non Metallic Box to secure Black Powder
   Visco or Safety Fuse
   Wet Sponge (made in construction section)
   Dry Sponge (made in construction section)
   2x 5 Gallon Buckets
   Written Permission to use selected firing range
   Powder Measure

Step 2: Fill one bucket with water. This water will be used to keep the mortar clean and so that it can be loaded safely. It is also is for putting out any potential fires.

Step 3: Set up Firing Line and Safety Area.  

Step 4: Wipe down Breech and Barrel with Wet Sponge. Be sure to thoroughly clean the breech.

Step 5: Wipe down Breech and Barrel with Dry Sponge

Step 6: Measure out desired powder charge, and load into breech.

Step 7: Load the Bowling Ball, the finger holes  should face upward. When loading, stand to the side of the Bowling Ball Mortar.

Step 8: Verify fuse burn time.

Step 9: Cut fuse to a length that will yield at least a 20 second burn time.

Step 10: Ensure that the firing range is clear, and that all spectators are in the Safety Srea.

Step 11: Insert fuse

Step 12: Ensure that the firing range is clear, and that all spectators are in the Safety Area.

Step 13: With loud clear warnings, announce that the cannon will be shortly fired.

Step 14: Ensure that the firing range is clear, and that all spectators are in the Safety Area.

Step 15: Light the fuse, and return to the Safety Area.

Step 16: Stay in the Safety Area until the ball has landed and come to a stop.

Step 17: Wipe down Breech and Barrel with Wet Sponge. Be sure to thoroughly clean the breech.

Step 18: Wipe down Breech and Barrel with Dry Sponge

Step 19: Place empty 5 Gallon Bucket over the Barrel of the Bowling Ball Mortar. As long as the Bucket is over the Barrel, the Mortar can be considered disabled and people can safely go in front of the Firing Line.

Step 20: Retrieve Bowling Ball.

Step 21: Repeat steps 4-21 as desired

[DH2]

Drawings:


















(sorry, the firing range is upside down.... dont know exactly how that happened)

[RocklockI]

Welcome DH2 , I'm not any help when it comes to BBM 's .

BTW the DH-2 is one of my favorite aero's of all time .

Gary

[Cat Whisperer]

THANKS!
This is a valuable addition to our forum to have all the info collected.
(We need to collect the links to other discussions and add them here.)
The only change I would make would be to add a statement to ensure that there was a full 2" of metal around and behind the 2" powder chamber.  That would make it consistant with N-SSA (and others) rules of construction.

[XxLT250RxX]

Step 21: Repeat steps 4-21 as desired

Very nice.  I may have to build one.  I love step 21!

[DarbinCo]

You will have to forgive my stupid questions but..

Why not machine your chamber to safety specs and fit it over the neck of the bottle to take advantage of the strong neck area? Or at least part of the neck area if you had to cut it down.

The answer could be simple, I just dont have a bottle handy to look at and cant find a close up picture of one.  

[dominick]

DH2,  Just a friendly suggestion,  I would not recommend for anyone to cut apart an EMPTY acetylene tank.  That is when the tank is most explosive when there is an amount af air mixed with the remnants of gas as would be the situation with an empty tank.  Dom

[Double D]

The tank needed is not going to be an acetylene tank anyway, it will be some sort of pressurized gas cylinder marked 3AA2400.  No other cylinder will work!!!

As Dom alludes, pay attention and learn how to safely cut one of these bottle before you start...

[Terry C.]

Never put a cutting flame to ANY acetylene tank, ever. Never cut into one with a grinder or chop saw.

Acetylene tanks are never empty.

You cannot store acetylene under any significant pressure in an empty cylinder, it will become unstable and explode. That is why regulating the line pressure is critical and should never excede 15 psi.

The cylinders contain a porous filler that stabilizes the gas, otherwise, it would be a powerful bomb with a hair trigger.

That's why "empty" acetylene cylinders are so heavy compared to other gas cylinders.

There is no way to insure that there is no residual gas in the filler.

The only conceivable safe way to cut an acetylene cylinder would be a band saw with a very slow feed and a flood of water-based coolant on the blade.

Personally, I would avoid them like the plague.

[DH2]

THANKS!
This is a valuable addition to our forum to have all the info collected.
(We need to collect the links to other discussions and add them here.)
The only change I would make would be to add a statement to ensure that there was a full 2" of metal around and behind the 2" powder chamber.  That would make it consistant with N-SSA (and others) rules of construction.

The measurements I gave for the chamber dimensions allow for 2 inches of metal on all sides of it. It is a 2"Dia x 2" Depth cylinder inside of a 6" Dia x 4" Depth cylinder.

I didn't point this out to the reader, but it does follow the standards and recommendations pointed out on this forum and from other locations.

Thanks


To accommodate, I added a half inch to the desired length of the breech.

[KABAR2]

Once the valve assembly is removed from tank and it is left that way for some time I would doubt there would
be any gas left in it, common sense would dictate removal of valve on any empty tank before cutting.

[Cat Whisperer]

...
The measurements I gave for the chamber dimensions allow for 2 inches of metal on all sides of it. It is a 2"Dia x 2" Depth cylinder inside of a 6" Dia x 4" Depth cylinder.
...
To accommodate, I added a half inch to the desired length of the breech.

EXCELLENT !!
(Depth of a drilled hole is traditionally the full-diameter depth, adding the 1/2 inch accomodates more material for the point.)

Agian, thanks - it's a great addition to our resources to have ALL the stuff in ONE place!

[DH2]

You will have to forgive my stupid questions but..

Why not machine your chamber to safety specs and fit it over the neck of the bottle to take advantage of the strong neck area? Or at least part of the neck area if you had to cut it down.

The answer could be simple, I just dont have a bottle handy to look at and cant find a close up picture of one.  

Not a stupid question at all.

To be honest, I couldn't find any clear safety specs on chamber of breech plug dimensions, and so was rather going off my own intuition as to what would be safe. I settled on the numbers and design I did because I figured that it would be easier for a novice builder, with little or no access to a machine shop, to make the barrel and breech this way rather than in a more complex fashion.

Also, in researching, I saw alot of other builds done the same way as this one is and figured that it'd be best not to mess with what works too much. 

[Cat Whisperer]

...
and figured that it'd be best not to mess with what works too much. 

BINGO !

That often beats trying to figure out specs with which one is not familiar and making calculations - only to get burned by what one didn't know or understand.

[dominick]

One of the welding suppy stores I went to years ago had posted a news article with photos of a car that was blown up by a small plumbers size acetylene tank leak.  The tank was in the car trunk over night and it had a small leak.  When the owner smell the odor of the gas the next morning, he opened the trunk with the electric trunk opener and the gas mixed with the air in the trunk ignited.  The car was only about three feet high in the photo and parts of the car were found on the roofs of houses about a block away.  Miraculously, he excaped serious injury.  THE TANK ITSELF DID NOT EXPLODE!  It was just the mixture in the trunk.  "Had the tank went off it would have leveled his home", the explosive expert said who investigated the incident.  The second photo in the article was the intact acetylene tank with the investigator standing next to it.  I wished I had got a copy of those photos.  They are a wake up call when working with flamable gas.   Dom

[Double D]

Actually there is some very clear safety guidelines for chambers and breech plugs found N-SSA rules.  You must keep in the mind the breech plug/powder chamber is a small cannon.  The barrel on the bowling ball mortar or any of these type mortars is simply an expansion chamber and a holding fixture for the ball.  The ball in this case doesn't go down the bore but sits on the muzzle of the cannon.  
 

[Cat Whisperer]

Acetylene is so unstable it does not occur naturally.

When in the tank, it is kept in solution of acetone, which is absorbed in a roll of felt-like material.

As mentioned 15psi in the manifold is HIGH.

One safety  issue is that it does not explode - it DETONATES. 

I can tell stories of doing and surviving some of those things labled 'don't try  this at home....'

SO, the tanks are different than the other compressed gas tanks.  Good advice - keep clear of acetylene.

[Double D]

Section 2: Construction
 
Step 4: Bore  a 2” diameter hole into one end of the breech plug to make the powder chamber. This hole should be bored to a depth of 2” This is the chamber that will hold the powder and direct it's expanding gasses to propel the bowling ball. WARNING: DO NOT MAKE THE POWDER CHAMBER ANY DEEPER OR WIDER THAN 2" AS THIS WILL RESULT IN A WEAKENED AND UNSAFE BREECH PLUG.
 

This correct but needs clarified.  The guidelines for the safe design of cannons as found in the N-SSA rules says that the wall thickness around the powder chamber must equal or exceed the diameter of the bore.   

So there is two ways to  look at this example.  The stated powder chamber is 2 inches in diameter and this is the bore.  So it requires a wall thickness of two inches which gives a total diameter of 6 inches. w + b + w = d.   2 + 2 +2 = 6.

Going the other way.  You have a piece of 6 inch diameter round stock. To determine the largest diameter chamber you can make just divide by 3.  6 inch round stock divided by 3  equals two inches.

Don't forget the bottom, it needs to be one caliber thick also,

 

[Cat Whisperer]

What we have here is an EXCELLENT document.
MINOR clarification is being beaten to death - that goes with the turf - with these toys.

A PDF file would be cool!

[Double D]

Even minor things can hurt or kill you!!

[DH2]

In the modified/clarified/updated document (which I'll post in .pdf format) I'll include more in depth details concerning why things are the way they are. The guide as it is currently written complies with the safety standards that I could find/discern without explaining or stating them to the builder. The reason for this is that the guide is intended for novice builders and I was more concerned with writing a safe, simple guide than I was with providing an in-depth education in artillery 101. I'll partially rectify this in the next iteration of the guide at the same time that I make the corrections in terminology and design that were pointed out earlier in the thread or by PM. Either that, or ill simply correct this document and create another one that covers custom design of one's own mortar instead of following a pre-made design.

Just our of curiosity, would you guys (and girls) rather see a pair of documents, one which shows how to make one pattern of mortar and the other that covers safe design of a mortar; or a single document that catalogs how to design/make/modify a custom mortar but includes plans for a relatively simple one?

[Cat Whisperer]

DH2 -  Thanks for your patience with us in this process!  You have done something no one else has - to collect the info in a clear, simple and easy to read document.

MY preference would be two documents - that enables others to add other single-topic documents to the collection.

[DarbinCo]

Those cylinders are like hens teeth here, tough to find on the cheap!

I could buy one for 375 bucks...... But I dont need one that bad!