Coffee Can Mortar

[John N]

I’ve saved up a bunch of 1 lb coffee cans which are 3.95” in diameter at the rims and 5.5“ tall. Filled with concrete, they should make a fairly substantial projectile. However the only commercially available mortar I’ve found in this size range is the British Service Mortar over at Wild Imports. Their seamed liners and questionable quality control are not particularly attractive.

I’ve been thinking about having a barrel locally built. I’d buy a 6” diameter piece of cold rolled 1018 steel, 10 inches long, and have it machined with a 4” bore, 6” deep, with a 2” x 2” powder chamber. The profile would be plain with no contouring. This would give 1” thick walls and 2” of metal surrounding the powder chamber.

To save machining costs, IÂ’d have the base partially rounded, leaving a 4” round flat base to attach the trunnion. As far as the trunnion, IÂ’m thinking of a 2.5” round of 1018, ten inches long, with the middle 6” “slotted out about ¾” deep to provide a flat section to mate to the barrel base, then either screw it into  the sides of the base or have it welded on.

I havenÂ’t approached any of the numerous machine shops in Baltimore with any plans, but there seem to be plenty around here capable of doing the work. I would build a suitably sized (read massive) Coehorn base. IÂ’m hoping barrel materials and machining costs stay below $1000.

Based on your experiences, do you consider this choice of material and design strong enough to safely fire 2 ounce charges of 1fg lofting a can full of concrete?  

Your thoughts or suggestions would be most appreciated.

[CAV Trooper]

John,

Sounds like it should be good. You have plenty of metal around the barrel and powder chamber. If nothing else, at least it'll be heavy!    Make sure to post plans and photos.

[dominick]

Check this out. This is about the right size tubing and bore . A bit much on the windage maybe, but it might be easier than boring a solid piece.  The only thing I would do different is cross pin the breech plug with a 1" diameter hardened pin. This should work for a mortar also.  
           
                 http://www.buckstix.com/HowitzerBarrel.htm

[Cat Whisperer]

My 4.55" mortar (to left <-----) is of 7"dia x 13" long with 8" deep bore with 2x2 powder chamber.  4140.

Yours should do just fine.  I conisder mine most over built.  Compare, though with some of the cast mortars  -  I think you're in the ball park.

An 8" piece of pvc pipe filled with concrete weighs in a 7.5 lbs and will go as far as about 350 meters.

A longer barrel will be more powder efficient and range worthy IF you need to do your urban redevelopment in someone elses neighborhood.  I recommend keeping to about 100 yards so you can see where the round falls.

[Cat Whisperer]

Oh yea, the trunion is CRS 1-1/2" diameter - two 5/16-18 SHCS countersunk into the trunion holding them on.

Trunion and tube weigh 103 lbs.

Note the slight rounding of the base of the tube - spherical would have been cool, but it really doesn't matter much.  Tube is grooved to hold the trunion - done on a milling machine.

[Cat Whisperer]

Check this out. This is about the right size tubing and bore . A bit much on the windage maybe, but it might be easier than boring a solid piece.  The only thing I would do different is cross pin the breech plug with a 1" diameter hardened pin. This should work for a mortar also.  
           
                 http://www.buckstix.com/HowitzerBarrel.htm

That's a well documented and well thought through project.  

I was thinking seriously of doing it (got sources for moderatly priced steel, know a certified welder, ...) but then 225 pounds!  

The good news is the doctor said I didn't open up that old hernia, just did something to a ligament or muscle.  It will heal soon.

[Double D]

John,

Unless you have some burning desire to shoot coffee cans why don't just build it to 6PDR dimensions.  You could make contact with one of the N-SSA guys out at Ft. Shenandoah and get some balls.  Why you could even use my mold and cast your own.

Check you PM

[Cat Whisperer]

.... Unless you have some burning desire to shoot coffee cans why don't just build it to 6PDR dimensions.  You could make contact with one of the N-SSA guys out at Ft. Shenandoah and get some balls.  ....  

Excellent advice, especially in the planning stages.  To me, the two primary considerations of caliber are: a) availability of ammo; and b) restrictions to original calibers by organizations (which may limit the uses and opportunities to shoot and value).

With my 4.55" bore I sometimes shoot the 46oz juice cans - a LOT of windage but they still go 100yds down range with smallish charges!

[guardsgunner]

The guys ay Ft. Shenandoah (the West brothers ) were selling complete 12pdr. set-ups (barrel, bed, balls, ect.)for $1000.00 a little over a year ago before the price of steel jumpped. I dont know what they are asking now but you might inquire on the N-SSA B.B.

[John N]

Thanks guys - a lot of information to digest and consider!