Building a custom sawed-off shotgun

In this post, we are going to look at building a short barreled (sawed-off) shotgun. Obviously, taking a hacksaw to any side by side shotgun will work, but it may also land you in jail. If you are in the United States, a sawed-off, or short barreled shotgun is subject to the National Firearms Act and requires a tax stamp for possession. If you have any questions on how to legally handle a project like this don’t contact me, please see the ATF’s (Bureau of Alcohol, Tobacco, Firearms and Explosives) website and contact them if you have any questions.

One of my friends had a CZ Hammer Coach shotgun he wanted to cut down. After he obtained the tax stamp from the ATF (allowing for possession), he sent me the barrels (I’m an 07FFL SOT CLASS 2) to machine down to the proper length. We were looking for a finished product that looked clean and functional.

Before we get to the project, please take a look at the following disclaimer:

The contents of are produced for informational purposes only and should be performed by competent gunsmiths only. and its authors, do not assume any responsibility, directly or indirectly for the safety of the readers attempting to follow any instructions or perform any of the tasks shown, or the use or misuse of any information contained herein, on this website.

Any modifications made to a firearm should be made by a licensed gunsmith. Failure to do so may void warranties and result in an unsafe firearm and may cause injury or death.

Modifications to a firearm may result in personal injury or death, cause the firearm to not function properly, or malfunction, and cause the firearm to become unsafe.

For this project, I ordered the following items from Brownells:

First step is to actually cut down the barrels. In this case, the finished length is already listed on the tax stamp. I used some blue painter’s tape to mark the length slightly proud of where I need to end up. I make this cut on the vertical bandsaw and dress it up with the belt grinder.

Unfortunately, the barrels don’t have a solid rib joining them, this was the first problem I encountered. Note the top and bottom ribs of the barrel are only attached to the outside. The empty space in the middle looks unattractive and is a potential weak spot for the barrels to split from the ribs if the soldering job wasn’t done right at the factory.

You’ll note the factory muzzle has a filler piece soldered in. It may be hard to tell from the images, but the barrels were closer at the muzzle then they were where I cut the barrel. I can’t simply cut this piece out of the muzzle and reuse it. I’ll need to fabricate my own filler block.

My first attempt was to make a filler from hand by cutting and filing the steel. I didn’t like how it came out. I decided to CNC machine a piece to fit. To design the filler block I took a picture of the muzzle and imported it as a canvas into Fusion 360, the CAD CAM program I use. Once there, I drew the part I needed and than scaled it to a known size (I measured the barrel diameter).

This is the solid model of the filler block after I drew it. I’m amazed at what Fusion 360 allows you to do with a bit of practice.

I programmed the part into my CNC mill and cut it from a blank of steel. While this was a more technical approach, I believe it was quicker than hand fitting the piece.

I had to make two filler blocks. The first one wasn’t tall enough, ending up about .025″ short. A quick change to the CNC parameters and I made the one above. The second part had a nice friction fit.

I inserted the filler block into the barrel. You’ll note I had already drilled and tapped the muzzle end for a 6-48 bead. In hindsight, I wish I had waited; no sense in having another place for solder to flow.

I coated the surfaces with a paste solder and soldered the block in place. Alternatively, I could have used traditional flux and solder and tinned the parts. Tinning is when you coat the parts in solder prior to assembly. Soldering barrels is a tricky operation, you never know what solder they used at the factory (different solders flow at different temperatures), plus the barrels are thin. Too much heat and you may separate the existing top and bottom rib. You may also note some of the surfaces have a white dusty film on them. This is from a soapstone stick, the soapstone prevents the solder from adhering to any areas you don’t want it to when it flows.

At this point I can use the file to bring cut the insert block flush with the barrels.

After the file, I followed with an abrasive cloth on a block, followed by a series of stones. You can see how clean the finished filler is starting to look. You’ll note some tool marks in the image above, these all need to be polished out before the gun is ready for finish.

CZ claims these barrels are coated in a black chrome finish. Whatever it is, it doesn’t appear to be bluing and is very thin and easily damaged. We decided to coat the tubes in graphite black Cerakote.

The finished gun looks and handles great! This is a hammered, dual trigger, side by side that looks like something from the past!