Custom Remington 870 Defense Shotgun
A couple of years ago we posted a step by step tutorial of a tactical shotgun build. In it, we took a beat up Remington 870 Express and turned it into a cutting edge tactical shotgun. Recently, we set out to build a custom defense shotgun based on a new Remington 870 Police Magnum.
The Remington 870 Police guns come off a separate assembly line at the plant. These guns are subject to a 23 station checklist, have a longer magazine spring, heavier sear and carrier sog springs, a parkerized finish, compressed metal trigger plate, and machined ejectors and extractors. From our experience, the fit and finish on the Police guns tends to be superior. Our base gun came equipped with a walnut stock and 18″ IC barrel.
We decided to make the following upgrades to the shotgun:
- Install ghost ring sights with a rail for optics
- Install an extended magazine tube (we prefer the handling characteristics of the one shot extension over the two shot versions)
- Install a white light for target identification
- Install a reduced length-of-pull stock
- Refinish in Cerakote
This article will chronicle our experiences building a custom defensive shotgun and is presented for information purposes only. We are careful to observe all safe firearm handling and machine shop safety practices during it. If you wish to attempt a project like this, please do so under supervision of an experienced gunsmith.
- Parts and supplies
- Disassembly of the Remington 870
- Rear ghost ring sight installation
- Front ghost ring sight installation
- Refinishing in Cerakote
- Reassembly of the Remington 870
Parts and Supplies
Special thanks to Brownells for providing the following parts and supplies for this project:
Disassembly of the Remington 870
This is our stock Remington 870 Police as provided. Walnut stock, parkerized finish and 18″ bead sight barrel.
With the safety engaged and the shotgun pointed in a safe direction we verify the chamber is empty.
With the chamber verified empty, we check the magazine to verify it is empty as well. At this point, the shotgun is safe.
The magazine cap is unscrewed from the end of the magazine.
The barrel is removed from the front of the shotgun. The left shell latch is depressed.
With the shell stop depressed, the slide can be removed from the receiver assembly.
The magazine spring retainer needs to be removed.
The magazine retainer is removed with the tool from our armorer’s kit. The tool is screwed into the end of the retainer so the retainer can be pulled out.
Using the tool from the armorer’s kit, the rear and front trigger plate pins are removed from the receiver assembly.
With the trigger plate pins removed, the trigger plate can be lowered from the receiver assembly.
A Magna Tip screwdriver is used to remove the two screws securing the recoil pad to the stock.
The stock removal tool is included in the armorer’s kit. The captured screwdriver blade, makes aligning the tool with the stock bolt easy.
The stock bolt is removed with the stock.
The fore-end wrench is used to remove the fore-end nut from the fore-end assembly.
The fore-end nut has two notches that are engaged by the fore-end wrench.
The fore-end wrench removes the fore-end screw.
Our Remington 870 Police is now broken down so we can proceed. Note: the slide and bolt assembly are missing from the picture.
Rear ghost ring sight installation
The Vang Comp rear sight requires the installer to drill and tap 4 holes as well as a clearance hole for the rear sight elevation screw.
The action is centered in our milling machine vise and the front edge of the receiver assembly is located. In this case we are using a mill and digital readout to measure and drill our holes, a drill press or even a hand drill would both work as well.
At the location of the first hole, we use a #2 carbide center drill to start the hole for the #19 drill bit.
With the #19 drill bit in the chuck, a through hole is drilled in each of the locations for a screw. The clearance hole for the rear sight elevation screw uses a #29 drill.
A spring loaded tap guide is placed in the milling machine chuck. The 8-40 tap and handle are placed below the guide and the quill is lowered to tension the tap guide. With Do Drill Oil lubricating the tap, the tap is turned a half turn and then backed off to break the chip until the hole is threaded.
With the clearance hole and screw holes drilled and tapped, the base is secured with the provided screws.
Front ghost ring sight installation
We elected to remove the bead base by heating it. Heat control paste is applied around the barrel behind the bead base.
Observing proper safety precautions, heat is applied from a MAPP gas torch to the bead base.
A set of parallel jaw pliers are used to remove the bead base from the barrel. Here you can see the underside of the bead base. Note the bead is on a tenon that extends into the barrel.
Using the rear sight of the receiver and a level, the front sight is aligned. A scribe is used to mark each side of the front sight.
The front sight will be secured to the barrel with high temperature Silvaloy 355 silver solder ribbon and Ultra Flux.
All mating surfaces need to be cleaned to bare metal with abrasive paper and coated in flux.
The front sight is held in place with this spring loaded sight soldering fixture. The spring provides constant tension on the assembly as the solder flows. Heat control paste applied behind the work area protects the rest of the barrel. The area is heated with a torch until the solder flows and then allowed to cool without quenching.
Refinishing in Cerakote
Soft iron wire is attached at all metal parts that are to be refinished.
Observing appropriate personal protective measures, the parts are degreased using TCE (trichloroethylene). The over spray is collected in a bucket. TCE is applied until it runs clear from the bottom.
Rubber stoppers are used to plug both ends of the barrel and magazine tubes to prevent abrasives from entering.
Metal parts are blasted with Aluminum Oxide media after they have been degreased. Any oil on the parts could become embedded in the media, causing adhesion problems for the finish. If you don’t own a blast cabinet, ask around. Most car guys have access to one.
After the parts are blasted with Aluminum Oxide, compressed air is used to remove any residual abrasive.
After the parts are degreased a second time with TCE, Cerakote is mixed and applied with an airbrush. The Cerakote is allowed to sit for 30 minutes after application.
Parts are hung in the curing oven and allowed to cure at 250F for two hours. If you don’t have a purpose made oven like this one, you can make your own from an old locker.
The Brownells curing oven is cool to the touch while the parts are allowed to cure at the appropriate temperature.
Reassembly of the Remington 870
Once the parts are cool to the touch we begin the reassembly process. The rear sight rail is secured to the receiver assembly with the provided screws. A small amount of thread locker is applied to each screw.
We decided to replace the wooden factory fore-end with a Surefire model with an integrated white light.
The new fore-end slides over the fore-end tube assembly and the the fore-end nut is tightened. The nut can either be tightened with the wrench from the armorer’s kit, or the wrench shown above which is supplied by surefire.
The slide and bolt assemblies are placed in the fore-end tube rails.
The entire fore-end assembly is inserted into the receiver assembly. The left and right shell latches need to be depressed in order for the assembly to slide into place.
The barrel is placed into the receiver assembly. The new non binding follower (green) is placed inside the new magazine spring and both are inserted into the magazine tube. Note: the shiny areas in the photo show the areas where oil was introduced during reassembly.
The Scattergun Technologies magazine extension is screwed onto the magazine.
The new Speedfeed’s reduced length-of-pull stock is secured to the receiver assembly with the supplied stock bolt. The stock tool from the armorer’s kit is used to tighten it in place. Over tightening the stock may prevent easy installation of the trigger plate. The recoil pad will be installed after the trigger plate is reattached.
The trigger plate is inserted into the receiver assembly and the front and rear trigger pin plate holes are aligned.
The factory trigger plate pins are replaced by screws included with our Mesa side saddle shell carrier.
The Mesa side saddle is constructed of aluminum. A piece of surgical tubing inside of the holder provides friction to secure the shot shells.
The front sight post is an M16 type. Vang Comp Systems used to supply a XS big dot style tritium front and no longer does. This set was equipped with the white bead shown (middle). We replaced it with an XS white stripe tritium front (right). The detent and spring prevent the front sight from backing out.
After installing the front sight detent and detent spring, the tritium front sight is simply screwed into place.
The recoil pad is secured with two Phillips head screws.
A razor is used to cut small access slots in the recoil pad. The screws are then driven home with a Magna Tip driver. Oil is used to prevent the screwdriver shank from damaging the recoil pad.
A 2 MOA Aimpoint H1 Micro red dot sight is secured to the rail.
Our custom 870 defensive shotgun is ready for the range.
For more information on the Remington 870, visit Remington’s website.
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