Tracy, have you looked at the CG of the projectile at 45 degrees? I think until the barrel gets long enough to support the projectile, it will fall off. I would think a couple this rods say 1/8" if rigid enough to support the weight, would be unobtrusive enough to not affect the test.
I just wanted to bring this forward so we don't loose your hypothesis in design,
... after many, many observations, it is most likely the blast effect and NOT acceleration due to pressurization within the bore, which causes a black powder mortar projectile to fly as far as it does. We agreed that, considering the short stature of most black powder mortars, it is most likely that a larger proportion of the projectile’s propulsion comes from the blast effect rather than gradual pressurization. We also agreed that it would be interesting to do a series of experiments to see if we could find out if this theory was true or not.
Mike and Tracy
DD, I have not seriously looked at this potential problem until about 20 minutes ago. Your suspicion is correct, the CG (center of gravity) is in front of the BDC (bottom dead center) of the coffee can, insuring that it will tip out of it's position and fall on the ground, especially in the Zero Cal. experimental mortar.
In this photo the machinists square vertical blade represents the bottom edge of the can and the combination square blade aligns with the can's side while at 45 Deg. You can clearly see DD is right. The CG will be in front of the can's BDC and tipping will result.
I believe the 1/8" rods can be placed at a shallow angle to the can's side to avoid "hooking" on the reinforced rim at the can's bottom.
IIRC y'all have already sliced up the tubes, but how about making one tube and a sliding-fit 'chamber-insert' for lack of a better term, then stack however many blocks underneath it as needed to get to the requisite bore length? Ignition might be a bit of a nuisance, but electric might do the trick.
Shred, while yours is a very unique solution to our "multiple build problem" and would work with very little fuss if an ignition system could be devised and a reasonable way to counter-balance the long tube with the projo extending out of it's top by almost one full length. This latter problem is a more serious one, because we are talking about this config having big time balance problems. Bolting to a thick steel circular piece about 30" in diameter would probably mitigate it or lashing to a piece of 2 X12 bolted to an old truck rim filled with 100 Lbs of lead ingots would fix it as well. If it were not for these draw backs, we would use it and call it the experimental, "Bottomless Well Mortar".
I think until the barrel gets long enough to support the projectile, it will fall off.
If you fire at an almost straight up angle, that would not be a problem and measuring height of flight simplifies the math of calculating energy.
Esteemed West Coast Moderator, I like this idea better than almost all others. Easy calculations, no sliding projos tipping off the chamber piece. I bet 5 shots for an average could be had in 1/2 the time of the 45 Deg. set-up. However, there is one problem and it's a serious one, not some euphemistic "Challenge" as in modern, Corporate, double-speak, lingo.
The method of measuring the height is the rub as I see it. Some of us still have those plastic, Apogee of Trajectory devices from our youth when we launched Big Berthas and Camerocs skyward with black powder, Estes Rocket Engines. The plastic device had sights which were to be kept on the ascending rocket, a pistol grip and a trigger which was to be pulled only after the rocket reached it's Apogee. Pulling the trigger pressed a clamp on the elevation indicator which was a little lead weight on the string or wire. I can't remember if the elevation scale was graduated in feet of height or degrees, but I do remember that you were to stand exactly 100 feet from the rocket's launch pad. Maybe the trig was done by Estes engineers and you had a direct reading for the rocket's height at Apogee, I can't find mine right now and can't recall. The device was unreliable as best and gave very approximate results. Besides, I need the exercise in walking out to retrieve the fired rounds during testing.
How far away would be a safe distance to stand during vertical testing? I won't run after lighting a fuse, so how many feet will I consume of the 10 sec. per ft. fuse in a 50 shot experiment? Really George, it's beginning to sound like your method is complicating my life with more computations and making it more expensive too. Cost of fuse, cost of a hard hat, etc., etc.
Tracy
P.S. Speaking of hard hats, one would probably do you some good if a 14 pound projectile unfortunately smacked you. Remember that discussion just prior to the first Montana Model Cannon Shoot? Someone wanted to measure earth tremors in the 11" French Monster Mortar's impact zone. Rocklock suggested that the happy volunteer wear a hard hat just in case the unthinkable happened and the 137 pound Water Jug full of concrete tried to occupy the same space as the tremor device operator at the end of the descending branch of it's trajectory from about a half mile up. I wrote at that time, "At least the brightly colored plastic will mark the spot where he WAS."
