Remington 870 3-Gun Competition Shotgun Conversion

Remington 870 3-Gun Ready: 24 1/4″ vent rib barrel, Scattergun Technologies Trak- Lock II ghost ring sights, Speedfeed reduced length stock, Nordic Components 5 Shot extension, Mesa Tactical barrel clamp and 8 shot side saddle.

Remington 870 3-Gun Build and Brownells make a Remington 870 competition ready

The following documents our experiences and is presented for informational purposes only. In order to make the steps easier to understand, we separated the choke tube and front sight installations into two different sections, this is why you may notice some photos are asynchronous.  

Looking at the old useless 12 gauge 28″ vent rib 870 barrel we t0ok in on a trade, it dawned on us that this might be the perfect start to a 3-gun pump shotgun.  With my PD trade-in shotgun in hand,  we began to plan.  Since we already had an 870 receiver with a Scattergun Technologies rear sight installed, we decided that we would add a front sight to our vent rib barrel.  Knowing a 28″barrel is way to long to effectively compete with, we decided to cut and crown the barrel flush with the end of a long 5-shot magazine tube.  The stock was an OEM full-length wooden beast from the 60’s, replacing this with a short model would get us on target faster.

This project will require us to:

  • cut and crown a barrel
  • intall interchangeable choke tubes
  • install a ghost ring front sight on a vent rib barrel
  • add a shot shell carrier, stock and extended magazine

For the conversion (less the removable choke tube installation) we ordered the required supplies from Brownells:

To install the removable choke system, in this case Rem Choke, we ordered the following tools and supplies from Brownells:
As always, we make sure our firearm is safe and empty before proceeding.

Cut, crown and front sight installation:

Mounting our 28″ vent rib and 5 shot magazine extension we determine where to make the cut.
The vent rib is brazed to the barrel at several locations. We will make our cut in front of it. Later, we will use this point to cross-pin our new front sight.
We mark our cut location with a piece of soap stone.
After removing the barrel from the receiver and securing it in a vise with a set of blocks, we use a hacksaw lightly coated with Do-Drill oil to cut the barrel on the waste side of the mark.
Using a large file coated with chalk, we carefully square the cut.
After getting it close, the Clymer facing tool ensures that the muzzle is perpendicular to the bore’s axis. This is one handy tool!
Here are the two front sights Scattergun Technologies makes; the 12-gauge model (top) and the 20-gauge model (bottom). You will notice that the 12 gauge model is designed to be installed over a bead base. The 20-gauge model is shortened, with a mortise in the back to allow installation over a vent rib. For this project, we selected the 20-gauge sight set for this reason.  Detailed Scattergun Technologies Trak-Lock II sight installation instructions can be found here.
With a hacksaw and a file, we remove the front of the rib so the front sight will fit.
Test fitting the Scattergun Technologies vent rib front sight. We will actually have the front of the sight closer to the crown of the barrel when we are finished. The small void will be filled with epoxy.
After thoroughly degreasing both the front sight and the barrel, we mix and apply the two-part epoxy. After wiping away the excess, we use a thick rubber band to clamp the front sight in place and allow the epoxy to set for at least 24-hours before cross pinning with a 1/16″ roll pin.
After waiting 24-hours for the epoxy to set, we secure the barrel in a vise and set up to drill a 1/16″ hole through the sight and the metal block supporting the vent rib. We then take a 1/2″x1/16″ roll pin and set it in place with a roll pin holder and roll pin punch.
Here is the front sight assembly pinned.

Threaded Choke Tube Installation:

Before moving to the threaded choke tube installation, it is critical to verify that the barrel is thick enough.  While it is possible to measure the outside diameter of the barrel, subtract the largest diameter of the choke and divide by two; shotgun bores tend to never be truly centered and the walls may actually be thinner then calculated.  To avoid this, we used a Manson barrel wall thickness gauge to determine if the walls were thick enough for choke tube installation.  More information on choke tube installation criteria can be found on Brownells GunTech page.

The Manson barrel wall thickness gauge measures the actual wall thickness of the barrel. This is a critical measurement that calls for the best tools in order for the threaded choke tube installation to be safely accomplished.
To install the removable Rem-Choke system you will need a reamer, tap and bushing. Choke tube reamer (center), tap (bottom) and bushing (top).  The tap will work with both Rem-Choke and Win-Choke styles, however; the reamers are different.
Choke tube reamer, with bushing installed and tap handle.
After carefully measuring the internal bore diameter (in this case .726″), we select the appropriately sized bushing for the reamer and tap. This is critical, using a bushing that is too small will lead to poor results.  To manually ream removable chokes, the reamer manufacturer recommends mounting the barrel horizontally in a vise.
Coated in Do-Drill oil, we begin the arduous process of reaming the barrel by hand.  This makes back boring a barrel look easy.  Every 10-revolutions, we removed the reamer, brushed off the chips and reapplied the Do-Drill oil.
Success! We managed to hand ream an interchangeable choke tube. We took two breaks to go online and check out the metal lathe we wanted. It didn’t seem so expensive at the time.


Prior to tapping the choke, make sure you note how deep you need to cut. Running the tap too far can cause problems.  Laying out a tube next to the tap allows us to determine the depth of cut.
We clean away any excess shavings and install the bushing on the Rem-Choke tap. The barrel is oriented vertically and the tap is lightly coated with Do-Drill oil. We slowly turn the tap and cut the threads. The manufacturer of this tap specifies that you should not back off the tap to break chips as is typically done. Tapping was quite enjoyable after the hard work of manually reaming.
After cleaning excess oil and shavings from the barrel, we lightly oil the choke and screw it into place using our Magna Tip Choke bit.

Finishing the Conversion:

Since the barrel and sights are in order, we can finish getting the gun ready for the match.

In order to provide additional support for the magazine extension, we used a Mesa Tactical barrel clamp.  This model has a handy little weaver rail to attach accessories.  Mesa also makes the 8-shot side saddle we chose.  While we prefer 4 and 6-shot model for defensive use, the 8-shell carrier will certainly prove advantageous in competition.

Finally, we selected an old favorite, the reduced length Speedfeed solid stock and forearm.  The smooth rubber butt plate, shorter length of pull, and aggressive corn cob forearm allow for quick target acquisition and rapid manipulation of the slide.  We are ready for whatever the match director has to throw at us!

Remington 870 3-Gun Ready: 24 1/4″ vent rib barrel, Scattergun Technologies Trak- Lock II ghost ring sights, Speedfeed reduced length stock, Nordic Components 5-Shot extension, Mesa Tactical barrel clamp and 8-shot side saddle.


Close up of the Nordic 5-shot magazine extension, Mesa Barrel clamp and Scattergun Technologies front sight.
The left side shows the Mesa Tactical 8-shot side saddle.