GB mortar questions

[Gungrubber]

Hello folks was directed over here by jeeper1. Got a few questions to ask about a mortar I am building.
first I made this mortar to fire with fff or ff powder the bore is 2.60 deep golf ball bore then has a 50 cal powder chamber the same depth to the touch hole it was machined from 3" solid steel 7" in length. I am thinking with the short bore and sub chamber and the thickness of the steel it should handle any powder charge it can take. it will also fire a 50 cal lead ball from the sub chamber. it will put a golf ball almost sub orbital without turning it into a mass of rubber bands. any one else ever experiment with this type of design? what would you folks suggest as max powder charge. It has been fired with up to 100 grs of fff. Probably won't ever go much over that.

Any help comments or observations appriciated.

GG

[jeeper1]

I suspect that launching a 50 cal ball out of the subchamber could be dangerous because of the distance it can travel (1/2 mile plus).

[Double D]

Reason to fire a golf ball mortar.

1. Smoke...yep it will do that

2. Noise...yep it will do that although not real load

3. To watch the ball fly, yep you can do that.

4. To watch the ball the ball land (Or to see how close you can get to a target}.

Which can you do at 100 FFG grs.

1. Yep

2. Yep

3. For a while

4.  You better be able too for safety sake.

In this case don't think max charge think how far do you want to shoot.

With a 1/2 chamber you can accurately lob a golf ball 30 yards with 24 Grs of FG. Start with that load and work up one grain at a time and see how far the ball will go  for specific charge until you determine the maximum range you want to lob the golf ball.  You don't need a chamber much longer the 3/4 inch for launch golf balls.  Anything longer is just unneed and a waste of powder if used.

Switlik's chart for safe loads Cannons which you will find at the top of the board under safe loads says max for  1/2 inch cannon is 50 grains.

As far as wall thickness the rule of thumb is one caliber in all directions around the chamber. So if your chamber is  1/2 inch your walls should be at least 1/2 inch and that includes in the breech end.

[Gungrubber]

Thanks for the comment's and help. Seems like I am good with the saftey issues as far as strength goes. Also in terms of saftey range wise. better than 3 mi before I would hit anything except trees or a stray chipmunk. I live out in the country a ways. Lot's o dirt roads around here. I have a few more questions #1 I have decided to make a sled type base Would 1" steel round work for the
Trunnions. if that is the correct term it being on the rear of the mortar rather than on the sides like a cannon. #2 should I mill the barrel out to fit the trunnion or the trunnion to fit the barrel and should they be bolted together or welded or doesn't it matter.
I will be working out the powder and range tables once I get the base constructed right now I was just testing the barrel.

Thanks again
GG

[jeeper1]

Depending on how you mount it to the sled base one inch could be enough. If it's fully supported it should be OK. If just the ends are supported then over time and use it would be likely to bow.  One and a quarter would be better.

[CU_Cannon]

One inch should be enough.  Unless you are fireing lead projectiles and have trunnions that stick out more than 4 in on each side I doubt you will bend them.  You should only need to extend the trunnions 1.5 in or so. 

If you have a significant amount of material behind the chamber I would mill a groove in the barrel and weld the trunnion in place.  If you do not notch the trunnion and weld it in place.