Posted on 09/27/2003 8:39:41 PM PDT by mhking
Ah, serendipity. Being in the right place at the right time.
As it happened, this fine and sunny September Sunday morning found me and a few others at the local gun range, sighting in- or trying to- some rifles. Some were cooperating, some weren't. A normal outing to the range, really...
Until this fellow pulls up and starts unloading a big 'ol hunk o' pipe.
I thought he was going to bury it as a new target stand or something.... 'til I saw the Bowling Balls. I then immediately knew it must be what some call a "punt" mortar! I'd seen similar handmade ones on the 'net and in magazines... naturally, we all completely forgot about our own rifles for the moment.
The Gun Range is a nice place- raised, covered shooting line, plenty of tables, well-kept grounds. The first line of targets is at 100 yards, with small berms and pipe target stands at 200, 300 and 400 yards as well, plus a trail/road to drive up to 'em if you need to. And at 500 yards, right at the base of the stand of trees off in the distance, is a full-size steel cutout of a moose, painted day-glo orange. Above, the guy with the mortar is pouring in some three ounces of Fg (coarse) Pyrodex black powder...
This thing is huge! Probably weighing some 150 pounds, half-inch-nominal wall pipe with a massive two-inch-thick breechblock welded on one end. The touchhole or fuse passage leads to a small "chamber" in the center that holds the powder in a single spot, rather than letting it cover the whole 8.5" bore.
Crude, yes, but it works. The owner is reluctant to do any additional welding on the pipe, for fear of making a weak or brittle spot, so he just stacks up whatever's handy to hold it, oh, 'bout there or so. This thing's so cool I want to make the guy some adjustable legs like the old 4.2" Chemical Mortar had....
Three ounces of Pyrodex, an old garage-sale-special bowling ball, an old chair and some sewer pipe... Fire in the hole!
He's not running, but he ain't dawdling either! Let's see, the fuse burns at about one minute per foot, there's about six inches there... dum da dum... carry the three...
HOLY FREAKING BATTLESHIP MISSOURI! By the time the shutter snapped, the ball was, in relation to this picture on your screen, about six monitors up and climbing. It was whistling. I lost track of it since I was trying to get the picture, but the guys say it cleared the treeline by probably another hundred yards.
Let's do that AGAIN! Rod out the fuse hole, make sure there aren't any errant embers, pull the mortar up out of the divot it created, weigh out another charge of powder, another bowling ball... This time I was watching downrange with the camera pointing at the cannon... Holy Creeping God, ladies and gentlemen! That ball was screaming out of there! I'd wager it landed over 600 yards downrange.
I should have brought out my Radar Chrony. I'd guess that ball wasn't moving over 700 fps, possibly as low as 400 fps, but jeez, think of the mass! That ball's what, eight to ten pounds?!? What's the Hatcher's Index of a projectile weighing fifty-thousand grains moving at 400 fps? "Body armor" against this thing is eight feet of dirt over a concrete bunker!
Think Grandpas' old thirty-thirty is a kicker? How about a hundred-plus-pound gun that pushes itself into the dirt six to eight inches each time it goes off? This is not a shoulder arm.
After all four balls were expended, we helped load it back in the guy's car. I noted that there were some divots from earlier shoots... he said he gathers up old balls whenever he can find 'em, then when he has a few, on a nice day he'll come out and blow 'wm downrange. Says it always draws a crowd. I said "so there's already a few balls out there in the swamp, eh?"
"Oh, more than a few, yeah."
He says he also has a short cannon that takes small tomato-sauce cans and another mortar that takes soda cans. The soda cans, it seems, don't hold together well- the force of firing blows the can off the concrete fill, which then blows up in the air.
Besides, he says, NOTHING beats seeing that bowling ball howl downrange as far as the eye can see.
I agree. :) The pictures don't do this justice; this is something every Tinker or gadget freak should see in person at least once in their life.
I would not use ERW or DSAW, the only thing that I would use is seamless. As to availability, it is good, but I would want to check the MTR's personally. It would also have to be X-60 at a minimum.
The diameter of a bowling ball is is the initial parameter that we have to work with. Being a relatively fixed number we have to work safely around this number. Pipe size appears fixed at ten inches. Our variable is the wall thickness. The variable that I do not have is the clearance between the ball and bore that is optimum. If someone could give me an idea as to the thickness of wadding that is best we can work from there.
We cannot perform a pressure calculation until we determine a fixed ball size. We would have to pick a particular Model ball and work with that ball. The small variance of diameter is critical for accuracy and safety (pressure) is the first hurtle that must be jumped.
Where do range balls go when they die? This is our first step in obtaining cheap ammo and is required before we go any further in designing a system.
Also consider a plate vs a cap for the reasons in the article.
If you use a plate instead of a cap the pressure will kill the system before stress is even an issue. It has to be a cap.
The less heat stress from welding on the pipe itself is paramount.
Setting up a proper welding procedure to minimize stress is not a problem. I envision eventually that we will determine an optimum barrel length and then work from there. The testing procedure will include X-Ray and hydrostatic testing. After the hydro the excess length will be removed and we will have no fears.
This could happen folks!!!
I think that between you and Squantos that I could actually live through this!!
;<)
Or did they use a non-standard cylinder?
Next time the mood strikes me, I will have to give that a try.
Interesting detonator for fireworks. Have the remeber that one.
See post 193. 1/40th the diameter of the bore, 0.12 inches for a 10-inch. I wouldn't use any wadding.
Apples to oranges. 2,900 psi is dealing with a sealed system and 85,000 psi is an open system. The first is sustained and the second is momentary. Do you think that a tank barrel can withstand 85,000 psi if sealed? My glock can withstand 50,000 psi if sealed?
We are trying to stick to apples.
Thanks for the info.
Tom Eaker
and interesting thread that follows, too.
...nowadays around these parts a kid "blowing up" plastic 2-liter soda bottles with a little water and some dry ice can get him a Felony Explosive Device charge and a big lawyer bill.
:-(
Stay Safe !
Stay Safe !
Wrap any pipe in piano wire, and it will withstand ANYTHING! Just ask me! (^; (Just stand clear of BOTH ends!)
Nam Vet
OK ! Stay Safe !
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