Modifying an 870, AR Style

Canadian Made Remington 870 Stock Adapters and Top Rails
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In this article, Guest Contributor Ryan Houtekamer of 2 Cent Tactical walks us through some Canadian made Stock Adapters and Top Rails for your Remington 870 Shotgun.

Today we’ll be looking at the S&J Hardware AR15 870 CQB MKIV and the Cadex Tactical Shotgun Butt Adapter with the 870 Top Rail. Like most things in the firearms industry, the exterior parts of any weapons platform are mostly a matter of individual preference; what I like some of you may hate, and vice versa. With that in mind I will be writing this article taking multiple end-user opinions into consideration. To provide a wide sampling, these opinions are from trainers, police officers, soldiers, and competitive shooters. This article will be broken down by features and the make of the stock and rail system.

Buffer Tube Attachment/Placement

Since the purpose of both of these stock systems is to provide a means of attaching an AR pattern stocks and grips to a shotgun providing customization options to the user, this will be the first part covered.

Canadian Made Remington 870 Stock Adapters and Top Rails

S&J Hardware
The S&J Hardware AR15 870 CQB MKIV buffer tube is set up as close to the axis of the barrel as possible which means that the force of recoil will act in more of a rearward direction which will help to lower muzzle rise with proper stance and grip. Out of the two designs, the height of the CQB was preferred when it came to getting a cheek weld while aiming through the Vortex RAZOR Red Dot. I was the only person who preferred the lower tube on the Cadex stock adapter, but that is likely due to me having a much larger head then average. The buffer tube is screwed on like you would normally attach one to an AR, it is then held in place by the use of a castle nut. With no rail attached however the stock sights of my shotgun are near impossible to use.

Cadex Defence
The Cadex Tactical Shotgun Butt Adapter with the 870 Top Rail were designed to meet the military’s requirements for placement of the butt and the angle of the grip. Cadex suggested a high tube setup, like what S&J produces, for a more natural sight picture when using a rail mounted optic, but the unit’s requirements were maintained. Even though the buffer tube is lower, the tube is parallel with the barrel and not angled. I preferred the lower height of the buffer tube; however others would have preferred a riser attached to the Magpul CTR stock to attain a better sight picture. When the top rail of the Cadex adapter is not in use the lower height of the buffer tube makes using the stock shotgun sights far more comfortable. Instead of using a castle nut to keep the buffer tube indexed vertically, Cadex went with a set screw which engages the milled slot in the threads of most buffer tubes. I found the set screw method really quick to line up and though I have used the stock system with only a set screw, for my own piece of mind I also use a castle nut. The area that the buffer tube is screwed in to is large enough that the castle nut doesn’t create an odd lip. Due to the Cadex quick release stock system, the adapter pushes the stock about 2″ further back than the S&J version. This should be taken into consideration if you are worried about length of pull, though this was not an issue with any of the people who used it, regardless of their height

Pistol Grip Attachment/Angle

With the use of AR stocks comes the addition of AR grips, both of which are angled differently as will be outlined below.

Canadian Made Remington 870 Stock Adapters and Top RailsS&J Hardware
The S&J stock adapter has a grip attachment that mirrors a standard AR grip’s angle, which means that any of your non-beavertailed grips will fit just like they would on your AR. For this build I chose to attach a BCM Gunfighter Grip because I prefer the closer to vertical angle of the grip and felt it would keep my wrist at a comfortable angle when soaking up recoil.

Canadian Made Remington 870 Stock Adapters and Top RailsCadex Defence
Of the two stocks I received the Cadex stock system arrived first and I had planned on using the BCM Gunfighter Grip on both builds, however due to the military units requirements the grip angle of the adapter was angled forward. When the BCM grip was attached it had a near vertical angle which felt awkward to hold so I attached a Magpul MIAD in its place. At first this angle was quite puzzling to me until I held it with the MIAD grip attached, which effectively turns normal AR grips into lower angled grips like the BCM Gunfighter. If you get a Cadex adapter make sure to order a grip with a normal rake (the angle of the grip) or you might end up with an odd grip angle.

Attachment to the Shotgun

S&J Hardware
The inside of the CQB is milled out to accept the standard 870 receiver nut that allows the stock to be bolted on. It comes with the appropriate length bolt and even an Allen wrench to attach it.

Cadex Defence
Cadex had to supply a shorter receiver nut with their shotgun adapter as the stock release system occupies the space that a normal nut would be in. To remove the nut from my shotgun I had to freeze it, and heat up the receiver allowing me to use a longer wrench to remove it. Once the old nut has been removed, the supplied receiver nut screws in and torques down effortlessly.

Top Rail Attachment

Both the Cadex and S&J stock adapters are available with and without top rail segments, allowing user preference to dictate using the shotguns iron sights, running a red dot, or a combination of red dot and flip-up iron sights. I found both rail systems in combination with the Vortex RAZOR Red Dot and Troy H&K Style Micro Flip Up Sights to be extremely easy to snap onto target and very effective to shoot slugs with.

Canadian Made Remington 870 Stock Adapters and Top Rails

S&J Hardware
S&J use two hex head screws that attach to the top of the stock adapter. The front of the rail attaches to the barrel securely with a clamp that tightens with a single hex screw. The clamp is able to be slid to any point on the underside of the rail to accommodate any sights or other obstructions.

Cadex Defence
The Cadex design is a bit different however. When the stock isn’t being used with a top rail, a filler sits between the adapter and the receiver plugging a rectangular hole. When a rail is intended to be used the stock adapter is unscrewed from the receiver and the rail support is put in place of the filler. The rail support is a curved section of metal that arcs onto the top of the shotgun receiver. It has two threaded holes in the top that bolt to the rail that goes along the top of the shotgun. This support must be attached to the rail prior to attaching the stock adapter to the shotgun. Care must be taken when putting the screws into the support, the longer one needs to go in the rear, otherwise you will have a screw coming up through one of the slots on the rail.

The barrel mount of the Cadex system is different from anything I have seen before. In order to attach the top rail, the magazine tube end cap must be removed. A threaded adapter is screwed on adding a non thread section with a shoulder on it. The barrel clamp is then slid over the barrel and the magazine tube adapter and bolted to the rail. The end cap or magazine extension can then be replaced. I will say this though switching between stock systems and removing the adapter was a huge pain in the ass. I ended up buying a strap wrench to accomplish the removal. Tightening the end cap or magazine extension ended up tightening the adapter which doesn’t have any real meat to grab with bare hands. Without a strap wrench, holes through it or a slot across the top it’s not a fun removal. If you have no real reason to remove the top rail then this won’t really be an issue for you. The barrel mount also has two sections on the top side of it to attach a long and short rail segment for light/accessory mounting.

Sling Attachment

S&J Hardware
Doesn’t come with any sort of sling mounting system. Pending stock choice you can use the QD stud in your stock for a one point setup (one points are preferred by me on a shotgun to keep the pump free of obstruction from the sling).

Cadex Defence
Cadex went with providing several sling attachment points on the stock adapter. You have left and right QD sockets built into the body of the adapter. At the front of the adapter is a removable insert that is either flush with the sides of the adapter or can have a left or right-sided sling loop. The top of the sling loop is bowed out to allow certain types of snap hooks to attach to it too.

Canadian Made Remington 870 Stock Adapters and Top RailsShooting Notes and Other Parts

S&J Hardware
Like it was mentioned earlier in the article the shooters preferred the height of the buffer tube on the S&J CQB system more than the Cadex when using the Troy or Vortex sights. Through all my photographs of both the adapters being used the S&J had slightly less muzzle rise and shooters were able to fire subsequent shots marginally faster. Part of this could be attributed to physics and sight picture/cheek weld. To shed a tiny bit of weight from the top rail a milled grove runs the entire length of the rail. This groove can also be used as a rudimentary sighting system if your sights are damaged and need to be removed. I advocate running a set of backup irons if you plan to use a rail of this design though. The rail could be used to mount a laser system to it like the LaserLyte RML Kryptonyte Center Mass, or a light on an offset mount.

Cadex Defence
The Cadex stock adapter has one major feature that the S&J adapter does not have. Through the use of an AR magazine release button on the right side of the adapter you can release the buffer tube and stock from the pistol grip section.

Canadian Made Remington 870 Stock Adapters and Top RailsCanadian Made Remington 870 Stock Adapters and Top RailsCanadian Made Remington 870 Stock Adapters and Top Rails

This allows one shotgun to be able to fill dual roles easier. With the stock removed and the shotgun paired with a short barrel it makes a perfect door breaching setup. The stock can then easily be attached to the shotgun for any semi accurate work that needs to be done. The stock hooks onto an internal bar and is rotated upwards to lock it in. If it wasn’t for the overall length of shotguns in the shortest possible configuration being 26″ in Canada to remain non-restricted I would have loved to pair this stock adapter with a 12.5″ or shorter barrel to make a true breaching gun.

Canadian Made Remington 870 Stock Adapters and Top RailsCosts and Conclusion

The saying time is money is especially true when it comes to machining. The longer one item is being machined be it through intricacy or just a slow operator the less other items that can be made. With the price of machines it’s hard to have hundreds of them all working at the same time. This is where the large price difference comes into play between the two stock systems. The Cadex stock and rail system are a bit more intricate, have pressed in threaded inserts, and more time on the machine adds to the total cost of the unit. It really all comes down to personal preference, budget and needs. If you’re part of a tac team and want to make a great breaching setup perhaps the extra money the Cadex costs is worth it to you. If you don’t require the ability to remove the stock easily then the S&J might be more your speed. Both systems are able to be purchased without the top rails if it’s only the stock and pistol grip you require. The S&J Hardware AR15 870 CQB MKIV retails for $276 CAD (~$260 US) while the Cadex Tactical Shotgun Butt Adapter and 870 Top Rail retails for a little over $500 CAD (~$470 US). Both make excellent stock systems and you can’t go wrong with either.

Shotgun Build Parts
To save people from having to scour various pictures of what is currently on these shotgun builds, I have provided a breakdown of the parts:

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