Bowling ball mortars

[50bmg]

I want to build a bowling ball mortar, using the large oxygen tank as the
barrel. I have seen bipods and baseplates used that looked like surplus.
My big question is, where can you find these parts at? I have seen parts
at the Ima-USA websight that were marked as 81 mm bipod and baseplate
but did not know if these would work. (like what size is the socket in the baseplate?) Anyone with info on parts or kits, I would like to hear from.
I have plenty of room on my farm to fire one of these.
Thank you for your help.
50BMG in In.

[Double D]

You might want to think twice about using base plates and legs from Stokes type mortars.  In order for your mortar to be considered exempt from licensing as a destructive device  and an antique it must be a replica of a mortar made prior to 1899.  The Stokes mortar didn't come along until 1914.

If you do build a mortar using base plate from the 81 mm or any of the other Stokes type, you run the risk of having an unpleasant visit with the folks at ATF.

It's easier to start right off with the building by making a pre 1899 mortar so there is no chance for error.  You can come up with some pretty neat designs allong this line.

[Cat Whisperer]

I want to build a bowling ball mortar, using the large oxygen tank as the
barrel. I have seen bipods and baseplates used that looked like surplus.
My big question is, where can you find these parts at? I have seen parts
at the Ima-USA websight that were marked as 81 mm bipod and baseplate
but did not know if these would work. (like what size is the socket in the baseplate?) Anyone with info on parts or kits, I would like to hear from.
I have plenty of room on my farm to fire one of these.
Thank you for your help.
50BMG in In.

50BMG - Welcome to the board.  While there are quite a number of folks that have built mortars patterned after WWI and later mortars there is a very real question as to whether or not they are legal.  The law specifically mentions manufacture (or replica thereof) onor before 1898.  We choose here to take the legally safe route and not touch designs that are newer.  However if you are so inclined you will find links to the sources for these on many of the popular Class 3 boards.  I would not be surprized to hear of someone getting into legal difficulties by not knowing what the law says and doesn't say.

The key feature you're looking for is inside diameter larger than a bowling ball - that takes an outside circumference of at least 29-1/8 inches.  Less will not do unless you want to turn down the bowling ball.

[50bmg]

Thank you for the advice, any good ideas where I can find a legal kit
for a bowling ball mortar? I wish NO trouble with BATFE! But this looks
like fun. I'll spend some for a legal device. when I saw the pics. of
surplus parts being used I thought Neat! But no longer thinking like that!
Thank you guys!!

[Cat Whisperer]

I don't know of anyone putting together a kit.  The tough part is finding the 29-1/8" circumference cylinder or turning down bowling balls to fit the more common cylinders.

[50bmg]

Tim,
 I've a large Oxy tank(334CF?) I have cut off the flat base and a bowling
ball WILL go down it. This tank is heavy! Don't know what they are
hydro-stat tested at. 3000psi+? I have seen pics of these used with fuse
hole drilled in tank just below the heavy guard piece by the valve.
It looked like a trailer hitch ball had been fitted in place of the vavle

[Cat Whisperer]

Being only in the process myself (read that: look for someone else's experience, not my theory) I know a few things.  There is a number on the tank that if you take it to the dealer can be deciphered to the nature of the pressure test done.  

My feeling is that the fuse hole should go through the thickest strongest part of the tank.

The idea of the Coehorn is that one can have a thick walled chamber that contains the highest pressure (at first) and then a thin walled tube to guide the round when the peak pressure has passed.

How is this done?  There are several ways.  What's best?  Hmmm....