This 12pdr Coehorn Mortar was built about 5 years ago. It was my first full scale mortar. I was lucky enough to have access to a large lathe, milling machines and welding equipment at the time.
Total cost for materials was about $300-$350. I would say that it took about 80 hours over the course of a year and a half to complete not including design time. It is a fairly involved project and requires a wide range of skills.
7.00” dia. x 12.63” long hot rolled 1018 steel (1 req.)
(cold rolled would have been better but hot rolled was cheaper)
2.25” dia. x 10.13” long steel (1 req.)
0.25” steel plate (2 req.)
2” x 8”x 8’ long framing lumber (3 req.)
0.50” dia. x 12” long steel bar (6 req.)
1.25” dia. x 1.5” long steel bar (6 req.)
1.00” square x 0.5” steel (6 req.)
0.75” square x 0.4” long steel (4 req.)
3/8” x 6” carriage bolt (4 req.)
0.13" x 2.00" flat bar x 2.0" long (4 req.)
0.25” x 2.00” flat bar x 10.0” long (4 req.)
0.25" x 1.63" flat bar x 4.75" long (2 req.)
Tools / Equipment:
Lathe (as big as you can find)
General hand tools
Wood carving tools
This is my first instructable so please let me know if there is anything I can do to make improvements.
Step 1: Background
I have had an interest in cannons ever since I was a kid. Several years ago I participated in a civil war reenactment and I was hooked. After doing some research I decided that a mortar would give me the most bang for my buck. I came across a small mortar called a Coehorn Mortar. The design was originally developed by the Dutch engineer Barron Von Coehorn in the late 1600’s. Variations of the design were used in the American revolution and Civil war.
My mortar is based on the 24 pdr Federal 1841 model used during the American Civil war. I decided to build mine as a 12 pdr. The size refers to the weight of a solid shot. The shot for a 12 pdr is half the weight of a 24 pdr but about 80% the size.
Technically my mortar is not full scale but at 12pdr I still consider it full size. The confederates did have 12pdr mortar but I liked the Federal design better.
I want to note two things before continuing. First, this mortar is not a toy. It is a very real artillery piece and should be treated as such. Second this mortar 100% legal. It is not considered a “destructive devices” and does not need to be registered in the US. For more information see the National Firearms Act, sections 26 U.S.C. 5845 and 27 CFR 479.11, both can be found on the ATF website.