Bowling Ball Mortar: Seeking technical feedback

Discussion in 'Cannon' started by Pyroflume, Aug 12, 2019.

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  1. Aug 12, 2019 #1

    Pyroflume

    Pyroflume

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    About six years ago, I purchased a homemade bowling ball mortar from a man who had experience constructing bowling ball mortars. The mortar is made from a gas tank and has a welded-on breach piece with a chamber that holds up to about 4 oz of black powder.

    I love the mortar but have toyed with the idea of building an improved mortar someday, and I’m looking for feedback about whether my ideas may be feasible.

    The one thing I really don’t like about my current mortar is A) how dirty it gets when fired, B) how it is susceptible to corrosion if not cleaned immediately (and even if it is cleaned well, since I live in a humid environment), and C) how heavy it is (it weighs 300 lbs, making it very stable when fired but also very challenging to transport).

    My primary question is whether any alloy of titanium would be suitable for a cannon? I am aware that titanium and steel have very different properties in terms of strength, brittleness, weight, deformation, fatigue, elongation, ability to handle stress, etc. I am also aware that titanium, for a number of reasons, usually makes a poor choice in applications with pressure spikes (e.g., as a rifle barrel). However, there are many different alloys of titanium and I am wondering if any of them might be suitable for use as a bowling ball mortar? The appeal of titanium is it’s lighter weight and tremendous corrosion resistance. (And yes, I know that titanium is very expensive and difficult to tool and manufacture...so my question at this point is hypothetical). If titanium is a poor choice for a mortar, what about stainless steel or some other metal allow that is more corrosion resistant than normal steel?

    Another question is about powder. Currently I use FG black powder in my cannon (up to 4 oz max). Would any less corrosive blackpowder substitutes be suitable to use with a bowling ball mortar (for example, blackhorn 209)? I’m aware that blackpowder and blackpowder substitutes have very different properties (in terms of burn rate, pressure spikes, etc). I think I already know the answer to this question but would appreciate hearing from anyone who is more informed and knowledgeable.

    Another question is about ceramic coatings for a steel bowling ball mortar. If I painted a bowling ball mortar in something like high-temp cerakote (designed to withstand temps up to 1800F), would that potentially protect the steel from corrosion? Would the coating stay on, considering the heat and pressure of firing the mortar?

    My final question is whether there are any reputable manufacturers or builders of bowling ball mortars other than Coaches Club Cannons (see http://www.coachesclubcannons.com/Cannons/Bowling-Ball-Mortar)?

    Also, I’d be very grateful for not getting flamed for asking “stupid questions” or being seemingly lazy for not wanting to clean my mortar. I ask these questions in earnest in order to become better informed and to promote safety.

    Thanks in advance for any feedback and advice!

    - Dave
     
  2. Aug 12, 2019 #2

    Loyalist Dave

    Loyalist Dave

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    Well first, A, B, and C, above describe the very nature of a very large, black powder mortar. Black powder is dirty (only when compared to modern powder). Black powder residue is corrosive. Black Powder mortars need to be stable when fired, thus their mass. It's tough to get away from those and still have a mortar, I think....

    Next, most if not all of the black powder substitutes are actually a nitrate similar to potassium nitrate, plus some charcoal or coal. They either reduce or omit the sulfur to make them less prone to deflagration and thus are no longer considered an "explosive" but merely flammable. If you take Pyrodex, and remove the sulfur and charcoal, but keep the graphite..., you get Black MZ, which the company says is virtually non-corrosive. It's probably the lack of sulfur. Maybe that will help you?

    Cerakote would help the exterior of the mortar resist corrosion, but I don't think it would last in the chamber or where the ball sits. I think the sudden spike in pressure would cause fissures, perhaps too small for the naked eye. These would lead to corrosion which would undermine the adhesion of the Cerakote. BUT you could contact them and ask. They'd know what it can and can't do.

    Have you thought of Stainless Steel? Not lighter, but it would help with corrosion. I think the mass you actually don't want to lose too much.

    Perhaps if you reduced the outside diameter THEN had it wrapped in carbon fiber filament? Perhaps that would hold the pressure, but drop the weight down enough for you ??

    LD
     
  3. Aug 12, 2019 #3

    Zonie

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    I'm going by memory and prices have increased greatly since I retired but as I recall, the unmachined titanium forging we used to make our centrifugal compressor wheels cost well over $1500 each. With inflation, that would be over $2400 today.

    These were about 11 inches in diameter and 10 inches tall.

    Titanium, in order to even began to stand a chance of being used as a mortar would have to be a forging. The likelyhood of finding one that would be the size you would need rates up there with finding a chicken with a full set of teeth. Tooling for making a large titanium forging could easily cost over $150,000.

    I think one of the new synthetic black powders based on ascorbic acid could greatly reduce the amount of fouling in your mortar. These powders are known for their clean burning and weak pressures. I'm sure they would be safe to use in your mortar and sometimes they can be found rather cheaply.
     
  4. Aug 13, 2019 #4

    Pyroflume

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    LD, thanks a lot of your response! Helpful information. LOL...yes, as you pointed out, A), B), and C) pretty much describe the very nature of a large black powder mortar. But perhaps with some technical innovation, I can reduce a little bit of A), B), and C)? I like the idea of stainless steel. I wonder who might be able to collaborate with me to brainstorm a design and build it? Unfortunately, I don't have the tooling, welding, and machining capability or know-how.

    - Dave
     
  5. Aug 13, 2019 #5

    Pyroflume

    Pyroflume

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    Zonie, thanks a lot for the info. You're absolutely right that titanium would be crazy expensive! But perhaps a titanium mortar would make an interesting family hand-me-down for generations to come? LOL. It's bound to last virtually forever. BTW, I still have to do some research to find out if its a viable idea, but high-strength 3D printing is now possible with titanium. If I remember correctly, it involves vaporizing powdered titanium using a laser. Anyway, apparently high strength aerospace parts such as rocket nozzles are being manufactured this way, so maybe it would be more feasible than forging titanium? Also, I'm really glad to hear I can probably start using a black-powder substitute that is less dirty. That will definitely help with mitigating corrosion, and I'm guessing that without sulfur, there is less likely to be the rotten egg smell that I have to endure as I drive home for hours.

    - Dave
     
  6. Aug 13, 2019 #6

    Zonie

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    IMO, the smell of sulfur goes along with shooting historic old guns. Without it, something seems to be lacking.

    Protecting your mortar from corrosion from black powder isn't that difficult. The various salts that are made when black powder burns are all water soluble so just thoroughly washing out the bore with water will wash them away.
    Then, all it takes is to apply a coating of oil to keep the oxygen away from the metal. An aerosol can of light weight oil will do that.
     
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  7. Sep 6, 2019 #7

    MarkG

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    I know the SpaceX SuperDraco is 3D-printed, but it's only running at about 1,000psi. I'm guessing a cannon is quite a bit more than that?
     
  8. Nov 29, 2019 #8

    M. De Land

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    I also built a Bowling Ball Mortar but mine is built from a steel oxygen bottle made of 4140 steel and cut off at 27 inches long.
    I built an inner barrel chamber that threads into the neck threads from the inside and a sealed ignition striker that fires musket caps from a lanyard line, threaded in the top part of the cylinder neck treads. No welds any where on the cylinder which make heat risers and tend to weaken the tube.
    The exterior threads on the cylinder ( for the cap) house the rear mount for the tube and the whole deal is mounted on a steel sled made of glue lams on the deck. The swivel tube base is held captive to the tube by a nut made from the protective cap on the big exterior neck threads. The base is then affixed to a 5/8s thick steel plate bolted to the glue lam deck. I'd guess the whole deal bolted together goes about 250 lbs but have never weighed it.
    The 16 lbs. balls are a pretty good fit but I always belt them with 3 inch wide vinyl plumbers tape to give them a snug slip fit.
    I've timed the flight from using 1500 grains of cannon grade Goex and from ignition until back to earth lasts about 17 seconds.
    The ball just about goes out of sight vertically and the finger holes make a lot of noise up and back. It looks like it will go a good 1/3 to 1/2 mile on the arch from what I can tell by ball retrieve on the four wheeler. Hard to find a clear place long enough to safely shoot it.
    If I don't loose the ball I get about 3-4 firing before it finally comes apart from all the stress on the plastic exterior.
    The tube has a screw traverse from the sled mount that goes from vertical down to about 17 degrees. The sled is a very good base as it is strong and heavy enough to brake the tremendous recoil without coming apart. I did have to change the 1 inch diameter by 9 inch long base pin this year as the old one was starting to bend in the middle and was hard to get out for transport disassembly. I made the new one of O-1 tool steel hardened and stress relieved.
    It takes me about 15-20 minutes to soap and water clean it with a garden hose and hand brush.
    The firing assembly I made from a Mauser rifle striker and spring. The sealed ignition coupled with the inner powder chamber makes this mortar about as safe and efficient as one can be made. I still use a 25 ft lanyard and try to stand behind a protective barrier of some kind at ever firing.
    Never use wading of any kind in these and leave at least 10 minutes between firings. I also developed a load harness that lowers the ball into the tube without exposing your arms and face over the muzzle. If it fired on you at loading, one would get a good flash burn to the side but would not loose there head, hands or arms using this loading unit.
     
    Last edited by a moderator: Nov 29, 2019
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  9. Dec 21, 2019 #9

    steam1993

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    Stick to bp. I tried pyodex in my 24 pounder, ball did not leave the barrel(lots of smoke), it came just under half way out and then went back down the bore. Will tell you it was at a event with the public watching, range officer got a good laugth out of it and asked if i could do it agin. I went and some got bp, then the ball went 100 yards down range.
     
  10. Dec 30, 2019 #10

    Scota@4570

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    Blackhorn 209 is a smokeless powder: using it may burst the tube. Only use real Black. Corrosion is not an issue if you clean the gun.

    The best bowling ball mortar I have seen was tuned from a ship's drive shaft on a giant lathe. It was very-very heavy but beautiful and extremely strong. The walls were about 6" thick. It looked more like the originals.
     
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  11. Dec 30, 2019 #11

    Zonie

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    Blackhorn 209 may not produce much smoke but it is not to be confused with a true "smokeless powder" like Bullseye, Varget, Unique, Red Dot, 4227 or the hundreds of other true smokeless powders on the market.

    Blackhorn 209 is made for muzzleloading rifles and black powder cartridge guns (that we don't talk about) and it is measured just like Pyrodex and Triple 7 synthetic black powders. That is, it is meant to be measured by "black powder volume" style powder measures.
    It is more difficult to ignite than these and that leads to the number 209 being part of its name. That refers to #209 shotgun primers.

    It is a powerful black powder substitute but it should be safe to use in a mortar. If I was using it, I would reduce the powder load maybe 15% under a typical black powder load just to be on the safe side.
     
  12. Dec 31, 2019 #12

    Scota@4570

    Scota@4570

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    In another thread, Mad Monk described Blackhorn 209 as a bulk smokeless powder.
     
  13. Dec 31, 2019 #13

    Scota@4570

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    Found it on another forum. Bill Knight posts as Mad Monk. He wrote:

    "I have been digging through draws and brain cells all afternoon. Here goes.

    The Alliant Black MZ is an ascorbic acid based powder. The oxidizer system is a mixture of potassium nitrate and potassium perchlorate. A little carbon black to color it black. This would replace the one previous ascorbic acid powder made with a big slug of perchlorate. I seem to recall it being called Black Mag. That operation was being run out a garage someplce when they had the perchlorate blow up and destroy the building with two deaths.

    The stuff that was a modified nitrocellulose powder was sold as Blackhorn 209. I suspect that the 209 designation meant only 209 shotshell primers would light it off.

    These ascorbic acid based powders have come and gone since the first one in the mid-1980s called Golden Powder. The inventor took on investors. This gave a number of people to exploit the patent on the "invention". After lengthy expensive litigation several people walked away with the ability to exploit the basic patent. And each one had a different idea on how to get it to work best as a firearm propellant powder.

    Bill K."
     
  14. Jan 17, 2020 #14

    jimairwin

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    I will not do your engineering for you, but assure I know a lot about this. There are a few different specs of gas cylinders suitable, size-wise, for making a bowling ball mortar or howitzer. Look it up. The heaviest is probably best, as its wall is thickest (though only by about 1/16th inch). Pretty hard to find, relatively, however.

    I built mine using a "medium" spec. cylinder I found in the weeds beside a gas station. I tested it using the valve as my fuse hole. It has a burst disc built in designed to burst under compressed gas service well before the barrel can blow up. It bulged, but did not fail under charges of over 4 oz of Goex 2fg and heavy balls. BTW there are two specs for bowling ball circumference/diameter. The larger is about 1mm larger than the smaller. If your cylinder is not quite round, this will make loading a larger ball a bit challenging.

    Also BTW the valve end is way stronger than the muzzle end. If you tap the threaded pipe threaded valve hole straight thru (to straighten out the tapered pipe threads), a heavy duty trailer hitch ball fits quite well.

    Be sure to keep the finger holes up. If they're facing the powder, some balls can blow apart. Sort of interesting effect, but not recommended.
     
  15. Jan 17, 2020 #15

    jimairwin

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    The clearance (windage) between bowling ball & cylinder walls leaves little clearance for coatings or fouling. This is fortunate, as this requires wiping the bore with a damp towel between shots so you can load the next ball.

    Cylinders come with an internal coating already in place. There's no room for anything more.

    Black powder fouling is NOT corrosive in or of itself. It will absorb moisture from the air, which damp material IS corrosive (will accelerate rusting).

    I have experience with "alternates" for black powder. DON"T F*** with it!
     
  16. Jan 17, 2020 #16

    jimairwin

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    Howdy "Mad Monk" Great to see your smoke signals again after so many years!

    Our experiments with ascorbic/nitrates based powders produced a lot of interesting information and pretty neat stuff. Unfortunately, the economics were way off for commercialization.
     

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