Attempt to make a cylinder fail (BB Mortar)

[Cannoneer]

If I got the story straight here, this guy wanted to demonstrate how tough these tanks are, to prove that the mortar he built is safe.

[brokenpole]

These guys need to be on mythbusters.

[KABAR2]

   They have invented a new way to install fence posts..........
The main question are:
1 ) Is the base just pluged or does it have a chamber?
2) How big is the chamber?
3) How is the chamber attached?
A standard bowling ball I believe weighs in at 14 to 16 pounds I wonder what would happen if they proofed it with two balls?

[Double D]

They did not take a single measurement.   How much expansion was there from pressure.

I do like there test and I do  like the mortar that they are building.

[Cannon Cocker]

I recognize the voice as one of our members (piutsteve) who has a nice fullscale Whitworth/milsurp rifle.  Here's another entertaining video of his.  http://www.youtube.com/watch?v=A7qWv_q2puA&feature=relmfu

[GGaskill]

For what it's worth, a cast iron shot of the diameter of a bowling ball would weight about 84 lbs, so even five 16 lb bowling balls at once would not equal one cast iron shot.  On the other hand, if they never use more than one 16 lb bowling ball as a shot, maybe they are OK.  Hopefully they will use cannon grade powder in the future.

[BoomLover]

Actually, Double D, they did take one set of measurements...they were "measuring", (sort of), the amount of powder they were putting down the tube...their goal was to try to blow the tube up, using as much powder as they could measure into it...they didn't achieve success.......at least that is the way it seemed to me.

[Double D]

Yeah, I saw the Measuring" of powder. They said it was triple F pistol powder.  Who distributes FFFG in a plastic bag.

The measure I was looking for of course was breech diameter

[Artilleryman]

Yeah, I saw the Measuring" of powder. They said it was triple F pistol powder.  Who distributes FFFG in a plastic bag.

The measure I was looking for of course was breech diameter

I have purchased GOEX fffg, ffg, fg, and cannon grade that came in 25 lb plastic bags.

[Cannon Cocker]

 
The main question are:
1 ) Is the base just pluged or does it have a chamber?
2) How big is the chamber?
3) How is the chamber attached?

I have a feeling there is no chamber which brings me to bring up something I feel needs to be discussed.  I have seen a lot of emphasis put on the making of chambers for bb morters on this board and it seems they may not be necessary.  I put this to Jerry Janik who is known for having possibly the largest collection of mortars and mortar rounds in the world.   He has a bb mortar with an extraordinary recoil system, pin fired ignition, and accurate elevation calibration capabilities, with no chamber.  He says they are unnecessary. 

[BoomLover]

Cannon Cocker, that is very interesting...I wonder if all those Civil War Mortars actually had powder chambers, or if they did just like Master Blaster did, throw it in there by the cup full? Intriging comment from your contact, Jerry.....

[The Jeff]

I have seen a lot of emphasis put on the making of chambers for bb morters on this board and it seems they may not be necessary.

You're right, they may not be necessary. But I know for a fact a bowling ball mortar with a properly constructed powder chamber and sensible loads is safe.

[Cannoneer]

Cannon Cocker, that is very interesting...I wonder if all those Civil War Mortars actually had powder chambers, or if they did just like Master Blaster did, throw it in there by the cup full? Intriging comment from your contact, Jerry.....

BoomLover,
The U.S. Model 1861 iron mortars (13-inch, 10-inch, and 8-inch) did not have sub-caliber powder chambers.

[Microboomer]

Cannon Cocker, that is very interesting...I wonder if all those Civil War Mortars actually had powder chambers, or if they did just like Master Blaster did, throw it in there by the cup full? Intriging comment from your contact, Jerry.....

BoomLover,
The U.S. Model 1861 iron mortars (13-inch, 10-inch, and 8-inch) did not have sub-caliber powder chambers.

Of course, unlike earlier mortars, the 1861 pattern mortars have ~1 bore diameter of metal around the entire bore length.
I'm guessing 1861 pattern bowling ball mortars are pretty rare, but machine one out of 1018 and it would be hard to question the safety of the design!
andy

[Double D]

 

I have a feeling there is no chamber which brings me to bring up something I feel needs to be discussed.  I have seen a lot of emphasis put on the making of chambers for bb morters on this board and it seems they may not be necessary.  I put this to Jerry Janik who is known for having possibly the largest collection of mortars and mortar rounds in the world.   He has a bb mortar with an extraordinary recoil system, pin fired ignition, and accurate elevation calibration capabilities, with no chamber.  He says they are unnecessary.

The recommendation of a chamber is a safety factor to get the one caliber wall thickness. The recommendation has always been made as a base line starting point.  If you have the knowledge you can build walls thinner. Most people who come here do not have the knowledge.   

The real question is, since you get adequate flight from a bowling ball, with a chamber, why would circumvent a safety factor and leave the chamber out.

Further  having possibly the largest collection of mortars and mortar rounds in the world.  and a bb mortar with an extraordinary recoil system, pin fired ignition, and accurate elevation calibration capabilities, with no chamber  does not tell me he has the engineering knowledge to build them safely.  In fact since he suggests a chamber is not need I tend to believe he lacks the knowledge in that area.

I am trained as a gunsmith-college level. I have knowledge in ballistics and metallurgy.    I have sufficient knowledge to know that the are metals out there that you can build mortar from with out a powder chamber. I do not have sufficient knowledge to know what metals that might be. 

If Mr.  Janik has the knowledge than I would like to hear his reasoning and criteria as it would benefit us all.  Just the fact he built a gun and it didn't burst does not make safe.   Get him to join us and explain, we would be more than glad to listen and have the knowledge.

Just for the record, if you read the cannon accidents reported here you will notice a common statement is "we have fired it for years with out a problem...."

[BoomLover]

Double D, I 110% agree that the main factor is "Safety"! No doubt about it! I built the Coffee Can Mortar to the specs you provided, and feel very safe with that design. Always factor in the added metal around the powder chamber, and the 1 caliber wall thickness just makes good sense. Besides, you being a college level trained gunsmith, I'd kinda guess you just might know what your talking about! By the way, I'm building the base along the lines of the 1700's French Mortar, Port Orford Cedar, hope to have it finished before you hit town on your drive-thru...BoomLover Jim

[Cannon Cocker]

Not trying to start an "ironball" argument here.  Just thought that given the "proof" that you can't blow up a bb mortar with such a light projectile, we may want to re-think the necessity of a chamber in all situations.  Not advocating either way.  You also have to consider that cutting a hole in the bottom of the tube and welding on a chamber if not done properly can also be a liability.  That connection I always thought could be a failure point.  There is no skill in screwing a bung plug into the bottom of a tank, and if the tank itself is possibly strong enough, you may be unknowingly promoting failure by suggesting that others do more complex operations that they may not be capable of doing with precision.     

[Cat Whisperer]

We each draw the line (for safety) somewhere.

Where I draw the line now is far different after seeing a cannon explode 12-15' away.

Draw it whereever you wish, for me the 1/3 rule is OK.

[Double D]

Not trying to start an "ironball" argument here.  Just thought that given the "proof" that you can't blow up a bb mortar with such a light projectile, we may want to re-think the necessity of a chamber in all situations.  Not advocating either way.  You also have to consider that cutting a hole in the bottom of the tube and welding on a chamber if not done properly can also be a liability.  That connection I always thought could be a failure point.  There is no skill in screwing a bung plug into the bottom of a tank, and if the tank itself is possibly strong enough, you may be unknowingly promoting failure by suggesting that others do more complex operations that they may not be capable of doing with precision.   

Take an objective look.

At first glance it appears very impressive watching them toss 32 ounces of BP down a tube a drop bowling ball on top and fire it off.

But to watch that test and say that test proves that it is safe to make a mortar with this thin wall tank is ludicrous. There is no measurement of the pressures.  There  no measurement  of how much the tank expanded.  There is no examination of the tank for fatigue after any test.   

The mere addition of larger volumes powder doesn't equate to massive increases in pressure only a larger volume of gasses generating pressure.   

I not sure what liability you are talking about when using a chamber. 

I think you fail to understand that with inner chamber, the chamber is the cannon.   The pressure tank is simply an expansion chamber and ball holder.  The pressure of firing is contained in the chamber.  When the gases exit the muzzle of the chamber they expand and pressure is reduced until they meet resistance from the wall of the tank and ball. There is still pressure in the barrel, it is just substantially under the chamber pressure.

Tossing a bunch of powder in tank is not a proof test.  Proof test are carefully calculated pressure to stress the barrel to   determine if it has flaws.  European (CIP) proof pressure is 125% maximum average working pressure with none of the pressure used to determine the average not exceeding 115% of the average. If the arm exposed to CIP proof does not fail, it passes proof and my used.    American (SAAMI) proof pressures are 140% to 170% working pressure depending on the arm and cartridge.  Generally designs are proofed and them measured to determine their dimensional changes. If the changes are with in acceptable ranges the design passes proof. If the changes exceed acceptable ranges, the gun fails proof.  The goal of proof is not to achieve catastrophic failure.    If the gun fails proof by catastrophic failure then it is seriously flawed. Guns fired to SAAMI proofs are kept for reference and not used. 

I do believe the sole purpose of the video was to film the destructive testing of the cylinder.  We don't know of they destroyed the tank as it was never checked.

[Victor3]

  You also have to consider that cutting a hole in the bottom of the tube and welding on a chamber if not done properly can also be a liability.  That connection I always thought could be a failure point.  There is no skill in screwing a bung plug into the bottom of a tank, and if the tank itself is possibly strong enough, you may be unknowingly promoting failure by suggesting that others do more complex operations that they may not be capable of doing with precision.   

 I've always thought the same about these things.
 
 Knowing the type of steel tank and chamber are made out of is important, along with a skilled welder who knows what type of rod to use to join those materials to ensure they'll never come apart. I also wonder how many chambered BB mortars have a crud-collecting gap inside where the OD of the chamber meets the tank wall.
 
 That said, I don't think I'd want to light the fuse on one that didn't have a sturdy chamber. I'm sure many (if not most) of these bbls are made from tanks that were past their service life and scrapped...

[Double D]

 
 I've always thought the same about these things.
 
 ... I also wonder how many chambered BB mortars have a crud-collecting gap inside where the OD of the chamber meets the tank wall.
 

That's a good point Victor.  In practice they don't collect crud.  The one that Southpaw has you can reach around the  the chamber clear to the bottom of the tank. 

Same thing with the plugs in  K.I.S.S. mortars I make, you would think the fouling would get between the wall and the plug.  It doesn't. 

The force of the blast from firing is directional out the barrel taking the path of least resistance and away for the bottom of the mortar.

I also suspect that is why the tank in the video doesn't burst.  The gases are taking the path of least resistant.   A loose fitting  16 lb bowling ball offer very little resistance.  The only massive force really demonstrated is inertia.  That is what buried the tube in the ground.

[KABAR2]

Has anyone tried to contact the maker of the mortar and the video to get more data? If there was or was not a powder chamber? if Dia of tube was taken before and after the last shot? etc.....

[Cannon Cocker]

I not sure what liability you are talking about when using a chamber. 

I think you fail to understand that with inner chamber, the chamber is the cannon.   The pressure tank is simply an expansion chamber and ball holder.  The pressure of firing is contained in the chamber.  When the gases exit the muzzle of the chamber they expand and pressure is reduced until they meet resistance from the wall of the tank and ball. There is still pressure in the barrel, it is just substantially over the chamber pressure.

I'm talking about the liability that the weld holding the chamber on to the tube does not have enough strength to keep it attached during firing.  I'm talking about the fact that the tube itself may have more inherent strength than Bubba's "solder joint". 

The chamber is definitely not the cannon.  The whole thing takes pressure.  Take one of your chambers and stand it up with a ball on top of it and see how far it goes.   You are making an assumption that sticking a thick chamber on a thin walled tube makes it safer.  You are making an assumption that the 1/3 rule which has inherent logic with straight walled tubes works the same way with bb mortars.  It doesn't.  Where are the statistics?  Where is the data?  How much pressure is on the weld?  Does a mortar with a chamber and a set amount of powder throw a ball further than one without one?  How much further?  If it's the same or close, then the the pressure in the base of that mortar is the same or close with or without a chamber. 

I'm not sure any gas tank cannon/mortar is safe no matter what you do to it.   Are there past postings where these chambered bb mortars were proof tested, then measured for failure, or is it's safety based on the 1/3 rule applied to an entirely different set of variables. 

"There is still pressure in the barrel, it is just substantially over the chamber pressure." 

[Artilleryman]

In reading the posts on this topic, we can probably sum it up in that there was an attempt to blow up a oxygen tank barrel, an overload was created and the tank did not fail, and we do not know what type chamber may have been used if any.  The problem that is that in the video there was no evidence of a proper inspection of the barrel afterwards.

If there is no evidence of any damage after a careful inspection it would appear that the barrel would be suitable for reasonable charges, but we could probably assume that at any rate since these types of barrels have been used for a number of years with no apparent problems.

[Double D]

   
The chamber is definitely not the cannon.  The whole thing takes pressure. 

I think you do not understand what is happens when a gun fires and especially a mortar.  In stead of trying to understand you are arguing. Let me know if you want to learn, I will be glad to explain.

[Rock6.3]

   
The chamber is definitely not the cannon.  The whole thing takes pressure. 

I think you do not understand what is happens when a gun fires and especially a mortar.  In stead of trying to understand you are arguing. Let me know if you want to learn, I will be glad to explain.

I'm interested in understanding what happens when a mortar fires, please educate me as I am actively listening.

[The Jeff]

Take one of your chambers and stand it up with a ball on top of it and see how far it goes.

Seacoastartillery have plans to do just that pretty soon. I for one can't wait to see the results.

[Double D]

   
The chamber is definitely not the cannon.  The whole thing takes pressure. 

I think you do not understand what is happens when a gun fires and especially a mortar.  In stead of trying to understand you are arguing. Let me know if you want to learn, I will be glad to explain.

I'm interested in understanding what happens when a mortar fires, please educate me as I am actively listening.

Gladly.

In a cannon, the bore is cylindrical, all one diameter.  The charge in the breech section sits behind the ball and is the some size as the ball. The charge when ignited turns to gas which expand in all directions at once.  When it meets resistance the pressure increases.  The pressure continues to increase until it is able to over come the resistance either from the walls of the chamber failing or the ball moves down the bore.  The gases continue to expand and push the ball down the bore.  Since the bore of a cannon is a cylinder the gases move as a focused bore diameter column pushing the ball out the bore.   As the ball moves down the bore, because the volume behind the ball increases the pressure of the expanding gases decreases.

In a cannon, the chamber and the ball are the same diameter and the column of gases pushing the ball is the same diameter.  The path of the gases is linear down the bore.

In the mortar/howitzer chamber, the chamber is smaller than the ball and the bore. The ball sits in front of the chamber.  Again when the powder is ignited it turns to gas which expand in all directions at once until it meets resistance.  The pressure continues to increase until it is able to over come the resistance either from the walls of the chamber failing or the ball moves down the bore.  In the cannon the column of gas decreased in pressure as it followed the ball out the bore.   In the Mortar/howitzer when the ball starts to move, the linear column of expanding gas decrease as the space behind the ball increase.  When the gases move out of the chamber and ball moves the gases encounter the larger diameter ball bore. The larger bore creates larger space for the expanding gases to fill.  When the gases expand to fill the larger bore the  pressure decrease even more.

It is not a situation of pressure going to zero, but it is greatly reduced.

This is why cannons generally  have greater velocity and range than mortars and howitzers.

[Cannon Cocker]

This is why cannons generally  have greater velocity and range than mortars and howitzers.

I thought it had more to do with reduced barrel length and reduced charges, (but I probably don't understand something).

 Large bore cannon of the 18th century had powder chambers.  Following your line of thought, how would the ballistics vary (in general terms of course) between two identical guns, one without a chamber, and one with a chamber.

[Double D]

I thought it had more to do with reduced barrel length and reduced charges, (but I probably don't understand something).

That's also correct.  That's the point.

 

Large bore cannon of the 18th century had powder chambers.  Following your line of thought, how would the ballistics vary (in general terms of course) between two identical guns, one without a chamber, and one with a chamber.

The chambered barrel should have  less velocity and shorter range.