Tactical Perimieter Powerhouse (TAPP): The Look and Feel of an AR in a 12-Gauge shotgun
By J.M. Ramos

There is an emerging class of weapon that is quickly catching on with the military and law enforcement who recognize its effectiveness as a weapon of choice in close quarter engagement. In the past, a grenade launcher was the most common attached secondary weapon to a service rifle dating back to the Vietnam days. In current conflicts, a 12 gauge pump action shotgun appears to be a more desirable combination given the close quarter type of environment and is among the latest breed of combat combos; primarily those that are to be used by sentries whose primary duties are to protect the perimeter of the base and other fortified installations. And, as a stand alone weapon, it has proven itself time and again in urban environments and other close quarter situations such as caves and tunnels.

Remington M870

Remington became solidly engage in the development and manufacture of military and police shotguns as far back as 1907 and introduced their first slide action sporting shotgun the following year called the Remington Repeating Shotgun Model 1908. A “Riot” gun version of this gun was called Model 10R. The military version of this particular model was used in the trenches during WW1 and came complete with a magazine extension, barrel shroud and a bayonet attachment. There were other similar models that superseded the Model 10 but none came close to the continued success enjoyed by the M870: a true bread and butter for the company. Introduced in the commercial market back in 1950, the popular model was designed by the company’s engineering team headed by Lexie R. Crittendon. The gun’s twin action bar was no doubt the most desirable feature of the gun and proved to be the strongest in its class. Shortly after its introduction, the M870 became available in two fighting shotgun formats: the M870R (Riot Gun) and M870P (Police Model). Both models were simply short barreled versions of the field grade sporting gun. In its early years, these models found limited success in the police and security market. However, it was in the mid 1950s that a quantity of the M870R with slings was purchased by the British Security Forces that were fighting Communist terrorists in Malaya that eventually influenced the design of future combat shotguns: slide-action and automatic alike. To date, the M870 remains as the world’s most successful pump action shotgun ever made. It is a top choice in the US military and highly revered as a defensive weapon by civilians and its field grade versions remain a top favorite among sportsmen and hunters alike. Not much has changed in the overall design of the M870. After over five decades of uninterrupted production, it has remained the king of scatterguns from which all other weapons in its class are judged. With the advent of ultra-modern tactical shotgun innovations of the new millennium, the gun’s well established form of over half a century may be about to change.

The “M412”

What makes the slide-action shotgun like the M870 an ideal combination for an M4 is its outstanding simplicity and robust overall construction. Being manually operated, its mechanics is less affected by most adverse climatic conditions, something a mechanically operated arm can be rendered unserviceable unless maintained regularly. While it is practical to keep the M870 as simple as possible to operate and maintain in the battlefield as a combination gun to a standard service rifle, it can also be upgraded to a primary weapon system for certain applications if desired.

Since the 1980s, there were few numbers of related accessories offered by independent companies for the M870: these being generally limited only to folding stock and fixed pistol grip furniture. Barrel shroud and magazine extensions are also offered but these accessories have been around since the Riot Gun versions of these guns become commercially available. The tactical gun market of the new era however has finally offered large varieties of accessories that are far more sophisticated and functional. It is particularly interesting that almost any available bolt-on device available for the AR rifle can now be fitted to the Remington shotgun with a little bit of work and imagination.

The availability of many exciting tactical accessories for the M870 revived the author’s long lost interest in this type of arm and the author’s goal was to be able to re-create the M870 to look and feel like an AR but most particularly with less felt recoil. What could be better than an M4 style M870 that feels more like a Short Barreled Rifle (SBR) than a nasty shooting 12 gauge scattergun. The possibility of creating this “M412” with trend setting hardware that can be truly appreciated by AR fans may have just become a reality.

While the market for tactical shotgun innovation has finally taken off, putting together the configuration envisioned in this project would take some imagination and figuring out what is needed and how the selected components are going to be put together to achieve the desired result without overdressing the gun or overspending unnecessarily. Bear in mind, the most expensive part is not necessarily the best. There are similar gadgetries out there that are far less expensive but do the job as well as the pricey ones. What really counts is how the components complement one another and how good they are put together. A gun project can only be considered successful if it meets the builder’s expectations and a true custom tactical arm must perform as well as it looks.

In the creating of the M412, some minor work will be required since not all parts selected are for the M870. Anyone with a little experience in gunsmithing will have no difficulty putting this specimen together. Police and military armorers can also learn from this project. Since most of these servicemen are already equipped and familiar with AR type weapons, it is much easier to train one who is already proficient with it especially with the feel and look that they are already accustomed to. Competitive shooters who favor the AR in their 3-gun matches will truly appreciate the M412 format in their quest for the top place. The M412 designation simply put a nice ring to the upgraded gun quite well. On top of the gun’s exceptional format, one can truly appreciate the added advantage of being able to incorporate almost any available device or accessory tailored for the AR to include BUIS sight, optics, varieties of stocks and forward grips, bipod, lights, lasers, etc. The sky is the limit. The arrangement is as good and as versatile as any ultra-modern tactical type AR out there. The big gun is now capable of exceptional accuracy with the aid of new generation sighting systems and handling characteristics never before experienced are achieved in this type of weapon.

Configuring the M412

The dominance of the AR rifle exterior format, primarily its straight telescoping stock design, has made tremendous impact in almost every type of popular tactical inspired long arms in the market today ranging from .22 LR to long range .50 caliber sniper weapons. This was a trend that soon expanded to accommodate police and military type shotguns to include the M870 and other popular US brands. Currently, the market has quite a few varieties of M4 style stocks marketed for the M870 as well as other US made pump action shotguns. However, it was not until the new CAA RS870 6-position collapsible stock became available that the author finally decided to undertake the project for four basic simple reasons: authenticity, quality, styling and price. Most similar stocks in the market are either too expensive, not authentic enough for a true M4 styling or simply poor quality. CAA (Command Arms Accessories) makes some of the finest accessories for the AR (and AK’s as well as other popular long and short arms) that are priced right for the average consumer. Along with the new RS870 stock, they also created the Shotgun Rail Adaptor (SGR1). This accessory is primarily designed to be mounted to the barrel as a laser/light mount. The writer sees a different use for it - a mount for an AR gas block front sight to match a flat top BUIS sight or a carry handle sight. For the carry handle sight, the CAA CH model that is used on flat top AR models fills the bill. The CH is less than half the price of most identical carry handle sights out there and is equally well made. The combination of the collapsible stock and Shotgun Rail Adaptor made it possible to create the M870 as close as possible to an M4 format sans magazine feed and self-loading operation. For a forward grip, the writer again selected a CAA product: the VG1 quick detachable combat grip. The VG1 matches the finger groove pistol grip of the RS870 stock. The combination of these ergonomically designed pistol grips is highly functional. For those “steady” shots, a bipod is simply an indispensable add-on in this tactical package. The CAA “Short Bipod” (BPOS) meets this requirement. This neat little bipod can be folded forward or rearward when not in use. When folded rearward, the pods rest snugly between the forend bottom rails yet it does not interfere when the arm is cycled manually. Complementing the compact M412 is CAA’s fully adjustable 1 inch Nylon One Point Sling, which allows easy movement of the arm when operating inside confined spaces. To accommodate the OPS sling, an end plate sling adapter (loop type) is assembled between the stock and receiver. Midwest Industries makes an excellent adapter and is available in a variety of styles.

Other accessories included in the M412 package are available from Brownell’s, Inc. These parts include the Wilson Tactical Picatinny Rail Forend. This replacement part is very well made from aluminum and features three Mil-Std 1913 Picatinny rails positioned at 3, 6 and 9 o’clock and are designed to accept forward grip, laser, light, etc. The Wilson accessory has the same length as the factory part and is securely retained on the action bar tube by the forend nut. Shooters with average or small hands may find the forend too bulky on the sides due to the over extended side rails. A simple solution to this is a forward grip such as the CAA VG1 or other similar handles that suits the operator’s preference. While it is possible to mount the bipod to the forend bottom rail, this will add more weight and bulk during operation. When the bipod is deployed, the forearm cannot be operated as usual since the gun is planted firmly to the ground. However, the author found that by holding firmly on the forward grip and pulling it downward to lock the bipod solidly to the ground, the shooter can simply move the gun back and forth with the rear grip following the movement with the shoulder resting steadily against the butt. This manual cycling action of the gun is quite comfortable and easy to get used to and quite fast. The gun is equipped with Scattergun Technologies (Wilson) one-shot extension. One special accessory found by the author in the Brownell’s catalogue to be a perfect mount for the CAA bipod is the 30mm Scope Accessory Rail made by Tactical Night Vision (TNV). This accessory simply clams to the magazine extension and can accommodate a light/laser or a bipod. In installing the CAA bipod to the TNV accessory, it is necessary to enlarge the first notch of the rail be used by using a 3/16 chainsaw file to fit the large diameter assembly screw of the bipod. (Note: do not over cut: the notch only needs minor widening. Keep the same depth.)

For a back up iron sight (BUIS), the writer selected one made by Yankee Hill Machine (YHM). These are very well made sights and priced right. Since the M870’s barrel does not rest as low on the receiver as on the AR, the YHM Forearm Flip Sight is the most compatible to the normal height of the Flat Top rear sight. The standard height front flip sight will be too high if used in this set up. The DPMS steel detachable front sight is a perfect match for the CAA Carry Handle Mount sight. The CAA sight is fully adjustable for both windage and elevation and can be raised if needed to get the perfect sight elevation alignment for the standard height of the gas block front sight. The YHM Forearm Flip Sight also worked well with the CAA Carry Handle Sight. To accommodate the BUIS sight to the receiver, the B-Square Saddle Mount was found to be most compatible having the longest forward extension. The longer rail allows the installation of the CAA Carry Handle Sight with an ample portion of the sight base forward clamp connecting to the front end of the B-Square mount. To install the YHM Rear Flip Sight to the B-Square accessory, the second notch at the rear must be enlarged with the 3/16 diameter chainsaw file to accommodate the large connecting screw of the sight. The CAA Shotgun Rail Adaptor assembled at the front end of the barrel has larger slots and do not require any modification to accommodate both the YHM and DPMS front sight. While some may consider a heat shield for the barrel unnecessary, it does offer some sort of protection especially for the busy shooter who enjoys shooting a lot of rounds in a single session. In this gun project, the heat shield was incorporated not only for heat protection and cosmetics but also as a mounting base for a forward rail extension that would allow low mount installation of Red Dots such as the Eo-Tech and other similar devices in front of the Carry Handle Sight. The most compatible accessory to act as a forward extension to the B-Square mount was the Havlin Mossberg M500R rail. This accessory is exceptionally well made and the price is unbelievably low for its overall quality. The heat shield made by Advance Technology has elongated slots, is well made and economically priced. The shield is shortened at the front to fit the shorter distance from the rear end of the rail adaptor where the front sight is mounted. In cutting the required length at the front end of the shield, a small tab was left at the top front end to fit tight underneath the Shotgun Rail Adaptor when assembled. The rear end of the shield had its own built in clamp and secures the part solidly at the base of the barrel. The Havlin rail is positioned precisely at the top rear of the shield to act as an extension to the B-Square rail and just about level with it. The forward end of the Havlin rail will need a tapered aluminum pad at the bottom to keep the part perfectly straight at the front since the forward end of the shield tapers downward. The pad is connected to the shield by a 6-32 screw assembled from the bottom. Separately, the front end of the Havlin rail is assembled on top of the pad by two 6-32 socket head screws on its pre-drilled mounting holes. When the Carry Handle Sight is assembled to the B-Square mount there is a fraction of the handle sight that extend past the B-Square part and locks with the Havlin rail connecting the two rails together as one. It’s a simple but effective set up. The added forward rail can now accommodate an optic and will no longer require dismounting the Carry Handle Sight before any extra accessory can be alternated.

One of the major drawbacks of the M870 design, at least at this point in time, is its magazine capacity. For a short barreled format with a 14 inch barrel, the most you can have ready for action is 5 plus one for a total of six with one-shot extension. Ideally, a compact ten-shot box magazine with double row compartment tapered to a single feed would be the perfect improvement for this battle tested shotgun. So far, the most one can do is to install a side saddle mount. These accessories vary in capacity from four to six and are normally assembled on the left side of the receiver. The author found the 6-shot Side Saddle made by Tac-Star to be a perfect add-on to the tactical package. The saddle is mounted to a thick aluminum plate backing. The extended portion of the saddle was removed and squared shortening the overall length of the part but still keeping the 6-shot holders. The front end of the saddle was secured to the collapsible butt stock through the QD push button sling swivel mount. A mild steel rod insert was turned and assembled through the mounting hole with its enlarged section at the base acting as a stop. A 6-32 socket head screw was assembled inside the center hole of the insert and connects directly to the aluminum backing of the side saddle. The saddle is secured to the rear of the stock via a drilled hole inside the second cartridge holder also using a 6-32 socket head screw. The assembly hole for this screw in the stock must be smaller and threaded for the corresponding retaining screw. The head of the screw will flush below the plastic part when tightened and stop over the aluminum backing when tightened. Any protrusion of the screw inside the butt stock must be cut flush so it will not interfere with the sliding movement of the part. The screw head will not be visible when the cartridge is inserted to the loop. This arrangement provides the operator that extra leverage for an instant supply of extra rounds when needed.

CAA can participate in developing a product in this category to complement their superb M870 accessories. The writer discovered their AR Picatinny Mag Pouch (MPS) can actually accommodate 3-inch Magnum rounds with just enough tightness to keep the rounds in place. Unfortunately, the pouch will only take 3 rounds and needs to be pushed by a rifle cartridge through a hole behind the pouch. A wide elongated slot on the exterior side that fit’s the thumb to push the cartridges forward and out will also work with the MPS. Unique with the CAA stock is that it has a built in side rail which can be moved on either side of the stock. It is logical for this company to develop and produce a 6-round magazine complete with spring loaded follower to push the cartridge to the lips as the operator unloads. The back side of the magazine will have a matching connector for the rail to hold it into position in either side of the stock.

The end result of this project is quite a rewarding experience. In summing it all up, not only did the M412 closely resembled the famous US battle rifle it emulated, but shooting this upgraded tactical powerhouse is now a joy to shoot and the dreaded shoulder breaker was finally tamed and looks better than ever.


Command Arms Accessories

76 Vincent Circle
Ivyland, PA 18974
Phone: (267) 803-1002
Website: www.commandarms.com

Brownell’s, Inc.
200 South Front Street
Montezuma, IA 50171
Phone: (800) 741-0015
Web: www.brownells.com

This article first appeared in Small Arms Review V12N6 (March 2009)
and was posted online on June 29, 2012


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