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Threading a Shotgun Barrel for Choke Tubes
by Roy Seifert

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Disclaimer:  This article is for entertainment only and is not to be used in lieu of a qualified gunsmith.  Please defer all firearms work to a qualified gunsmith.  Any loads mentioned in this article are my loads for my guns and have been carefully worked up using established guidelines and special tools.  The author assumes no responsibility or liability for use of these loads, or use or misuse of this article.  Please note that I am not a professional gunsmith, just a shooting enthusiast and hobbyist, as well as a tinkerer.  This article explains work that I performed to my guns without the assistance of a qualified gunsmith.  Some procedures described in this article require special tools and cannot/should not be performed without them.

Warning:  Disassembling and tinkering with your firearm may void the warranty.  I claim no responsibility for use or misuse of this article.  Again, this article is for entertainment purposes only!

Tools and firearms are the trademark/service mark or registered trademark of their respective manufacturers.

I regularly participate in local 3-gun matches where one of the guns is a pump or semi-auto shotgun.  I wanted a shotgun that would reliably feed the Aguila short 12ga. shells so I could fit more in the magazine tube.  I purchased a Winchester 1300 Defender, which came with a cylinder bore barrel.  Apparently, it was for use with 00 buck loads.  Shooting target loads with this barrel made such a wide pattern that I couldn’t knock down steel targets at 15 feet!  I thought the best solution to this problem was to thread the barrel for choke tubes.  Since I had a Winchester shotgun, I decided to thread the barrel for Winchoke tubes.

There are four steps in the process for threading a shotgun barrel for choke tubes:

  1. Measure the barrel to see if there is enough metal for threading.
  2. Fit the bushing to the inside of the barrel.
  3. Ream the inside of the barrel to ensure it is uniform.  This also removes any existing choke.
  4. Tap the barrel for the appropriate choke tube.

The left photo shows the necessary tooling, which I purchased from Brownells.  From top to bottom are the tap, reamer, and pilot bushing.


Step 1:  Measure Barre
The instructions that came with the tooling stated that the barrel had to have a minimum outside diameter of 0.845”.  My barrel measured 0.900” which gave me plenty of metal.

Step 2:  Fit Bushing
The bushing helps keep the reamer and tap centered in the barrel.  I purchased a universal bushing that was a bit too large.  I took the barrel and bushing over to a friend who has a lathe and he reduced the diameter of the bushing just enough so that it would fit in my barrel.  He offered to ream and tap the barrel for me, but I didn’t bring the tooling with me!

Step 3:  Ream Barrel
I mounted the barrel in a padded vise and used a tap wrench to ream the inside of the barrel.  I was surprised at how much metal was removed.  I used plenty of cutting oil to lubricate the reamer, and removed the reamer to clean off chips regularly.  I stopped when the last step of the reamer was touching the front of the barrel.  The reamer had removed enough metal that a step was left in the barrel.  This step was where the end of the choke tube would set leaving a flush seam between the barrel and the choke tube.

Step 4:  Tap Barrel
Again, I used a tap wrench and plenty of oil to tap the threads for the choke tube.  I turned the tap maybe 1/2 turn, then backed it off one full turn to break the chips.

After the barrel was tapped I thoroughly cleaned it with brake parts cleaner, then oiled the barrel.  I applied some choke tube lubricant to a modified choke and installed it in the barrel.  Now, with the modified choke, those metal targets fall every time.


Part Number





12 ga. reamer



12 ga. Winchoke tap



12 ga. universal pilot


   © Copyright 2008 Roy Seifert.