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)
  Milling Machine
  Band saw
  Drill press
  Welding Equipment
  Skill saw
  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.
<p>That is AWESOME!!!!</p>
I to am a Reenactor. And the color that they said was a match seems to me like it it. It looks as if it matches the pain used on the light artillery mounts wheels. <br>Good luck in future Battles and may your projectiles fly true.
I have a small cannon and I use home made quick match to set it off. I also use 1/4&quot;lengths braided cotton cord soaked in a potassium nitrate solution (slow match) attached to a long stick to light the quick match. Once I make the quick match and it dries it is cut in 3&quot; lengths and then placed inside small diameter paper straws. I don't have the recipes handy for the quick match right now but you can find it on the internet. Any trouble locating it you can e-mail me and I&quot;ll see if I can dig it out. Great build by the way, they are a riot to shoot.
Or you could just go to the nearest Phantom Fireworks (or the equivalent) or find a fireworks stand around independence day, and buy 3ft of fuse for little over a dollar.
Quick match and quills would have been used prior to the Civil War. That&rsquo;s not to say that they would not ever be used but the primary ignition method would have been friction primers. Any cannons below 100 lbs are too light for friction primers. The pull is usually 10 to 15 lbs. Friction primers can be purchased for about a dollar each. At some point I would like to try to make some of my own. <br> <br>I have made quills using a strip of tape and a straw. You take some 1F or 2F powder and sprinkle the sticky side of a piece of tape about 4&rdquo; or 5&rdquo; long. This is then placed in a paper straw. About a half inch or so is left sticking out of the top. The finished quill is placed in the vent and ignited with a slow match. The idea is that, once ignited, the flame travels very quickly between grains due to the air space in the straw. Ignition is almost instantaneous.
I found the recipe for the quick match and it is pretty simple. You will need a box of corn starch and some black powder. First dump the corn starch onto a cookie tray and spread out evenly. bake at 350 degrees for an hour stirring occasionally. This converts the starch to dextrose which is your glue. Now mix the dextrose with your blackpowder at a ratio of ten parts black powder to one part dextrose, add enough water to make a slurry. I use a disposable plastic container with a lid. Punch a hole in the lid the diameter of your fuse material. I use cotton kite string doubled. Push the string down into the slurry and let it soak awhile. Then push the string up through the lid and draw out slowly. I have found that 3 foot lengths are managable. Lay these out on a nonporous surface to dry. When this is dry cut to the length you need and insert into the paper straws. Make your fuse about 1/4 inch longer than your straws. Store in an airtight container to keep moisture away. The straws are small diameter paper art straws available at hobby or art supply stores. I don,t know if these are period correct but they are cheap and work like a charm.
Nice work
I would like to thank everyone for the encouragement. I have a few other designs that I have built that I&rsquo;ll post if there is interest.
Damn, this is awesome!!!
Wow. You make it sound so easy too.<br> <br> Fascinating project - I too would like to see a video, assuming you can find something safe to fire, and somewhere safe to fire it.<br> <br> It must've been hard work making one of these in the 17th.&nbsp;century. At least you don't have to worry about the whole thing blowing up because of an undetected flaw in your barrel.<br> <br> Thanks for sharing that with us.
This is pretty awsome! great job!
was there anything you needed to register this as? if you are American, a &quot;firearm&quot; is classified as an object using combustion of some type(black powder, explosives, etc.) to propel an object through the air(the one exception is a spud gun for various reasons) and i believe most firearms must be registered somehow. Awesome project anyway. Great job!
If the mortar was classified as a destructive device it would need to be registered and a permit would be required.&nbsp; But, per the ATF it is an antique firearm and exempt from registration. <blockquote> <p> <strong>From 27 CFR 479.11:<br> Antique firearm</strong>. Any firearm not designed or redesigned for using rim fire or conventional center fire ignition with fixed ammunition and manufactured in or before 1898 (including any matchlock, flintlock, percussion cap, or similar type of ignition system or replica thereof, whether actually manufactured before or after the year 1898) and also any firearm using fixed ammunition manufactured in or before 1898, for which ammunition is no longer manufactured in the United States and is not readily available in the ordinary channels of commercial trade.</p> </blockquote> <p> This also falls into the &ldquo;don&rsquo;t&rsquo; be stupid&rdquo; category.&nbsp; If you act suspicious you will be treated as such.&nbsp; It is unlikely that every municipality will know all the laws in detail.&nbsp; I have a copy of the federal regulations in my powder box.&nbsp; If there are ever any questions I can bring it out for reference.&nbsp; It is also still a firearm so all local regulations need to be followed.&nbsp; This is not something you could fire in you front yard anytime you want.&nbsp; I would recommend contacting your local police department if you have any questions.</p>
In most state even a BB gun or Pellet gun is classified as a fire arm, mostly because of their high potential of causing injury or death (especially in the high power pellet guns that use only compressed air for it's propellent, but can kill rabbits, coyotes, etc.) Florida even classifies paint guns as a fire arm, but BB guns, Pellet guns and Paintball guns do not have to undergo any registration. Many of these look exactly like a real gunpowder/blackpowder gun and using one to commit a crime draws the same sentence as using real gun. <br> <br>Some states also classify cross bows and draw bows as a fire arm.
Nice just like the ones made in the 1800s
I think you might want to fix the spelling of your title. The low-explosive material used is <b>black powder</b>, with a &quot;d&quot;. <br><br>As written, your title coupled with the discussion of the device's use by the Confederacy is tinged with irony :-/
Fixed, I don&rsquo;t know how many times I&rsquo;ve worked on this and not caught it. Thanks for catching that.
No worries! It's a great project :-)
This is great - I'd love to see a video of it firing as well, though.<br><br>I've stood near black-powder cannon firing &quot;blanks&quot; (actually a lump of wadding an straw), and you don't so much hear them as <em>feel</em> them go off.
You always know just what to say Kiteman. Nice build jeanluc.
Simply awesome! i plan on making a mini cannon when i get my lathe.

About This Instructable




Bio: My full time job is being a husband and a father to my three children. My paying job is a mechanical engineer. Every once in ... More »
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