On another forum on a thread I had started back in 08 someone wrote the following and thought this was the safe way of building and firing a mortar 
I did not mince words in a responce to him........"If you REALLY want to play mortars, you can locate a bipod from SAMCO or SARCO or Sportsmans Guide or somebody and make your own.
Get a short cut-off piece of drill stem (3-4feet). You want the female end that has a big bell with internal threads. Then heat up several pounds of lead/wheel weights/range backstop detritus, etc until it melts. stand the tube on its tail on a piece of steel plate or concrete or something impervious to heat and pour about six inches of lead into the tube. The melted lead will form around the threads in the bell of the bottom of the tube, and will not fall out. It should also be flush with the bottom if you poured it right. Then, drill a 1/8th hole in the side of the tube about an inch above the level of the lead. This is the fuse hole. Attach the bipod. Then, pour some black powder in it, drop a beer can full of flour in, stick a six inch piece of cannon fuse in the hole and light it, then run at a right angle to the direction it is aiming and hide behind cover.
My son and I did this when he was two years old or so. The reason you run for cover at a right angle is that the recoil can propel the whole mortar backwards at quite an impressive rate. We couldn't find ours after the first shot: it had gone backwards through a small horse barn and was about 20yrds away. He is now in the DMZ in Korea with an a U.S. Army Artillery unit--go figure.
Be sure to leave some room around the projectile for high pressure gas to escape. One of the features of black powder is that it becomes more powerful when confined. Give it plenty of room to vent out the end of the tube. That safety precaution along with the tremendous strength of drill stem should suit your purposes.
Of course, you should hide behine COVER not cealment when it goes off, just in case. And, you should inspect after each shot for signs of over pressure, like cracks, bulging, etc.
Have fun; B-safe!"
My responce below:
Sir what you discribe is foolhardy at best! at worst you may get yourself or someone else who follow your directions killed or maimed!
DO NOT LISTEN TO HIM! I have been building and using cannon and mortars since 1980 and I still have all my fingers, limbs etc. why?
because I do not use shoddy sub standard building methods when I build something. if you must inspect your tube for "signs of over pressure, like cracks, bulging etc." you are using too much powder to begin with! At least your son is learning the proper way to handle artillery in the army and not the BUBBA method.... please if you must try to blow yourself and your "mortar" (pipe bomb) up please do it else where and don't instruct the unkowning on the wrong way to do things.
Allen <>< I hope I didn't come across as mean or nasty.........
