Firing results for the “Pin Ball Machine” Mortar

[Rich44]

I call it the Pin Ball Machine Mortar because the size is the same as those steel balls used in the pin ball machines.

Having a full size Mortar would sure be a lot of fun, but let’s see. I would probably have trouble moving one by myself. Do not have a place to fire it or have the money to feed it. But if you can live with a smaller model mortar of maybe 1/6 size, well it opens the door for some experiments and fun in shooting and understanding of range correction. Will admit if that piece of metal had been larger a Golf Ball size Mortar would be ideal.

I do not have a crony, so having knowledge of what the velocity is would be nice to know. Sometimes if enough information is given a ballistic formula might fill in the missing information. Have a very short video showing the 3 different shot loads being fired and will give details.

The barrel of the mortar was set at 55 degrees from horizontal (instead of the more normal 45 degrees) to help keep the landing zone closer, for all shots.

Special wooden/steel shot with a ribbon attached was used on shot 1 and shot 2.
All wooden projectiles were found after firing.

Shot 1 = 25 gr. 3f powder with 1.2 ounce projectile and landed 55 yards from firing point. Have no idea how high as was unable to see. Mild bang and low recoil.

Shot 2 = 50 gr. 3f powder with 1.2 ounce projectile and landed 80yards from firing point. Have no idea how high as again was unable to see. A solid bang and slight more recoil. Give me 2 points for having the patch return.

Shot 3 = 50 gr. 3f powder with 2.85 ounce steel ball (1.062 dia.) projectile and landed I hope by now. Have no idea how high or far (over 100 yds.) as again was unable to see. Very sharp bang and much more recoil.



Is there any chance with the given information, that the height of the projectile can be determined and or the speed in fps? Or a good guess? We have weight, angle and distance.

From research of other people firing golf ball type mortars they are getting 200 - 300 fps.

I am amazed at the lack of flame coming out the vent hole. With the smaller powder chamber and large short bore the pressure just does not build up as much as a cannon length barrel.

 

[russellshaffer]

Very nice and lots of fun.

 

[Rich44]

Well this “Trajectory Calculator” Created by Hanna Pamuła, PhD seems to give a better picture rather than a wild guess. My 80 year old eyes just could not see the projectile in the sky. How accurate this calculator is not sure. But it does give a good relationship of a mortar trajectory. Put in the known angle of fire of 55 degrees and kept changing the FPS till the projectile went the correct distance that happened 240 feet. Looks like maybe the steel weighted wooden projectile that was used went about 85 feet in height that day. Well that is as good of answer so far. It was interesting to note that the 45 degree setting results in the most distance. Get the idea that most mortars were set at that 45 degree angle, and then the range desired set by the powder charge. Anyway mortar fire is very interesting and a good mortar man had to have some experience under his belt.

https://www.omnicalculator.com/phys...on?c=USD&v=a:0,v:90!ftps,angle:55!deg,h0:0!ft

 

[zulu]

Rich44,
Ballistics are out of my area of expertise but this was interesting. Thanks for posting.

 

[Rich44]

Out to the range with my small Pin Ball Machine Mortar on a nice sunny day. This posting is probably only for the people interested in the physics of mortar shooting. The clearing for shooting is kind of short at this spot, so I reduced the charge to 23 gr of 3F and still using 55 degrees from horizontal for the elevation of the mortar. My first shot went 67 yards or 200 feet. The two formulas that I use to understand the flight path are:

https://www.omnicalculator.com/physics/trajectory-projectile-motion

and

https://www.omnicalculator.com/physics/time-of-flight-projectile-motion

In the trajectory cal I plug in the numbers 55 for the angle and 0 for the initial height. And then keep adjusting the FPS number till the range equals the 200 feet. This will give me a close estimate of the velocity being 83fps. Also tells the height of shot as being around 70 feet.

Using the next cal Time of Flight I can enter the same numbers with the known speed of 83 and get the time from the bang to it hits ground again. In this case around 4.2 seconds. The video actually verifies this as the thud of the 1-1/16 inch steel ball can be heard after the bang at around 4 sec.

This is all new learning for me and kind of fun, but I can see if you are not into math it might not be interesting at all. But thanks for looking.

A funnel for loading powder to the chamber.