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My First Tagger:
Build the Casing

With most of the materials available, I started to lay out placement. I first worked on a full-size paper drawing, and quickly moved to a plywood silhouette. After cutting some pieces for the receiver, I realized I was missing a speaker from the layout, and chose a mylar-cone 3 inch model (perhaps a little larger than needed, but I didn't want to make this too quiet). It also turned out that the battery was just a tiny bit too large to fit into the square hollow formed by the two U-channel receiver pieces. A bit of fiddling and thinking, and I'd modified the concept to put the battery and speaker in a hollow stock. Instead of the nifty XM8-style adjustable stock, I'd have a wooden stock that could be adjusted by adding spacer pieces at the butt.

full scale copy and plywood silhouette
The full-size copy and the plywood silhouette.

With that change, one of the three aluminum receiver pieces that I'd cut earlier was too short to use. The other two became the new upper and lower receiver shells.

Stock

I cut and glued the stock up from two pieces of 3/4 inch birch plywood, with a piece of 1/4 inch birch plywood to form the outer side surfaces. One of the side faces (the left one, that would be against a right-hander's cheek) was glued into place, and the other face was attached using furniture bolts with blind nuts. The wrist of the completed frame was cut down to fit inside the 1-1/2 inch U-channel, and some small pieces of that were screwed on to keep the bearing surfaces of the stock from wearing loose too quickly. A plate of 1/4 inch birch plywood was added over the butt of the stock. The stock turned out rather fatter than I'd have liked, but it is no thicker than an AR-7 stock.

partial stock stock with contents stock assembly
The partially built stock, empty. The stock with contents. The stock assembly.

In the hollow area inside the stock, I glued some blocks to keep the battery from sliding around. They held the battery rather well, with it only able to lift out in one direction. That movement was blocked with a short piece of strap steel, well smoothed, held down by a pair of screws. Since the battery can be recharged in place, and the battery should last for more than 24 hours of play, I don't see a strong need to make the battery easily removable. The speaker was supported with a plate of 1/8 inch ABS plastic, with a hole to secure the speaker's drive coil. The 4P4C telephone handset connector for the sensor wire was placed between two blocks, and secured with a piece built up from several layers of ABS plastic chem-welded together. A rectangular hole was filed to shape for the connector. The wires for all of these components pass through a 3/8 inch hole drilled through the wrist of the stock.

Lens Tube

I made the lens tube of 1-1/2 inch PVC tubing, using a connector sleeve to hold the lens in place. It works the same as the 1-1/2 inch to 2 inch connector recommended on the Miles Tag website, but gives a longer tube forward of the lens. I wanted that extra length so that I could shape the tube to evoke the sweeping curve on the front of the XM8. The curve is clearly not the same, but it looks better than a tube that ends vertically. I painted the interior of the tube and connector sleeve before assembly, since I didn't want to risk getting paint on the lens. To fit the lens tube into the tagger, I prepared a piece of 1-1/2 inch by 1/2 inch U-channel by cutting down a section to fit the connector sleeve. The sleeve was just a little too large, and I flattened the underside so that the entire tube would be supported by both sides of the U-channel for its entire length.

lens tube IR LED mount and bezel LED mounting disks LED mount in place
The lens tube, before cutting to length. The plywood IR LED mount, with bezel. The plywood IR LED (top) and muzzle LED (bottom) mount. The IR LED mount in place.

To hold the IR LED at the centerline of the tube, I cut a 1-1/2 inch diameter disk of 3/4 inch plywood, added a small plate of 1/8 inch aluminum, and mounted the LED bezel in the center. The plywood disk was slightly wasp-waisted to make it easier to slide in the tube, and to ensure that the bearing surfaces keep the best possible concentricity and alignment. I improvised two screw terminals on the back side of the disk to keep from having to unsolder and solder when replacing the IR LED.

After cutting three slots (to allow focussing of the IR LED after the casing is assembled), I mounted the plywood disk using 3 wood screws. Unfortunately, even with pilot holes, the disk split along a ply line. It seems that plywood isn't the optimal material for this purpose. I removed the hardware (bezel, LED, screw terminals) from the plywood, and made a replacement disk out 1/8 inch thick ABS plastic. I glued 4 plies together and drilled a 1/2 inch hole, sufficient to clear the mounting nut and lock washer of the bezel. I then added one more ply, with a concentric 5/16 hole to mount the bezel. I rough cut the disk to a little over-large for the PVC pipe. Using a 1/2 inch rod as a holder, I used my drill press as a lathe to shape the disk to size with a rasp. Pilot holes for the screw terminals and mounting screws worked well.

With an IR security camera we had in the house, I focussed the lens assembly. The mounting screws, when loose, are usable handles for the disk, so I don't need to reach into the lens tube to move the disk. At night, using the longest stretch of clear view in the house, I was able to get a pretty good focus.

Lower Receiver

I built up the grip with a central spine of 3/8 inch aluminum, and 1/4 inch ABS plastic grip panels on either side. Some very rough shaping with a hacksaw, then rough shaping with a large half-round rasp, and sanding with emery cloth gave a nice dull finish with a pretty good feel. I attached the handle to a floorplate of 3/8 inch aluminum with two 10-32 bolts, tapped into the handle's central spine. The trigger guard was bent from a piece of 1/8 x 3/4 inch aluminum bar, and then filed narrower and to a more elliptical cross section for the portion under the trigger. A slightly undersize slot was cut in the aluminum grip spine to take the end of the trigger guard, and it was forced into place and staked to keep it from working loose.

disassembled lower receiver grip panels magazine and well
The parts that make up the lower receiver. The plastic grip panels. The magazine and magazine well.

The trigger was laid out as a cardboard mockup first, and tested against the switch, grip, and floorplate. The blank was cut out of the 3/8 inch aluminum plate using an electric jigsaw, then shaped with rasp, file, and emery cloth. The finger hook was rounded and smoothed more than the rest. The trigger was shaped to pivot above the finger hook, and has a forward extension that bears on a microswitch mounted in front of the trigger pivot. Since the microswitch return spring was too light, giving a trigger pull under a pound/500 g, a stiffer coil spring was placed over the microswitch. The trigger and microswitch are mounted to the floorplate with two lengths of aluminum angle. The trigger pivot is a length of 3/16 inch steel rod passing through the trigger mount and trigger, kept in place by the side walls of the lower receiver.

trigger assembly lower receiver
The trigger assembly. The nearly assembled lower receiver.

The cosmetic "magazine" was built up of five pieces of 1/8 inch ABS plastic, chem-welded together and sanded for a matte surface. The magazine extends up to the floorplate except on the rear. The magazine well was built up around the magazine from the same plastic in the same way. The entire assembly is attached to a pair of brackets, front and rear, hidden inside the plastic, and these brackets are tapped for bolts that come down through the floorplate. The reload switch is mounted in a square hole on the right side of the magazine well, placed similarly to an AR-15 magazine release. I scraped a shallow vertical groove in the side of the magazine, and built up a small fence around the reload switch, for cosmetic reasons. The wires from the reload switch pass through a hole in the floorplate above the magazine.

The floorplate is attached to the lower receiver, a piece of 1-3/4 x 1 inch aluminum U-channel, with three bolts. The receiver was cut away above the floorplate to make room for the trigger mounts. The rear of the receiver was shaped to fit the stock, and the front of the receiver was shaped to match the upper receiver. A slot was cut away from one edge to match the slot on the upper receiver, mimicing an ejection port.

The front of the lower receiver is attached to the foreend with two countersunk 10-32 flat head machine screws. The back of the lower receiver is attached to the stock with one countersunk 10-32 flat head machine screw. These holes were drilled while the upper receiver, stock, and foreend were assembled, to ensure the alignment.

Upper Receiver

The upper receiver is a piece of 1-3/4 x 1 inch U-channel aluminum, cut with sloped ends to match the lower receiver. A slot was cut in the right side to mimic an ejection port, and a hole was cut in the top of the receiver to pass wires to the LCD display in the sight tower. The main circuit boards is attached to a plate of ABS plastic that is, in turn, attached to the inside wall.

The first design for the sight tower, later abandoned, was based on three parallelopiped aluminum posts. The posts were drilled and tapped on top and bottom; the bottom attached to the upper receiver, and the top attached to a bar of 1/8 x 3/4 inch aluminum. The rear and middle posts were enclosed in a housing of ABS plastic, which was also the mount for the LCD display. The sight tower looked good, but wasn't parallel to the lens tube, and was inherently unstable in axial alignment.

first sight tower second sight tower front post housing sights
The sight tower
(first attempt).
The sight tower posts (second attempt). The housing for the front post. The sights.

The second design of sight tower is based on three right trapezoidal aluminum posts. Each post was cut from bar stock, milled square on the drill press, and then drilled and tapped for two 10-32 machine screws on the bottom. The upper receiver was drilled to match, with the front and rear posts countersunk to keep the screw heads from interfering with the stock and main circuit board, respectively. Around the rear and middle posts, I built a housing of 1/8 inch thick ABS plastic, which holds the LCD display. A 1/8 x 3/4 inch aluminum bar was attached to the top of the three posts as a handle and sight base. Aluminum "iron" sights were attached with a single countersunk screw each above the front and rear posts; the single screw allows a little rotation for windage alignment. After sighting in, I added a little penetrating LocTite (green) to keep the screws and sights from moving.

The foreend is attached to the front of the upper reciever with two 10-32 round head machine screws, which are hidden beneath a cosmetic housing built from several pieces of 1/8 inch thick ABS plastic. This housing also closes off the rear of the lens tube. The stock is attached to the rear of the upper reciever with two countersunk 10-32 flat head machine screws.

Foreend

The foreend of the tagger is based on a pair of 1-1/2 inch U-channel pieces, bolted together back to back. The upper piece is 1/2 inch deep, and cradles the lens tube. The lower piece started out as 1-1/2 inch deep. I cut the height down a little so that the assembly would nest into the upper and lower receiver, and then angled the remainder of the lower piece to a pleasing slope.

building up the foregrip cosmetic barrel muzzle brake muzzle
The foregrip, being built up of layers. The cosmetic barrel's attachment. The fluorescent acrylic muzzle brake. The muzzle end.

I placed the piezo buzzer (backup sound device) and the config switch inside the lower foreend. There was room enough, and I thought that I could get away with using a toggle switch instead of a keyswitch, if I put the toggle switch somewhere where it would be necessary to disassemble the casing before accessing it. All this was because I'd forgotten to order a keyswitch. The buzzer bolted to the aluminum channel directly, and the config switch is in a simple improvised ABS mounting.

The underside of the foreend is closed up with a foregrip made of a three-layer sandwich of 1/8 inch ABS plastic. The first layer is cut to fit inside the channel, and the other two rest on top of the channel edges. The front was built up onto the foregrip, and a hole was cut for the cosmetic barrel. The foregrip is rounded and sanded, and held on by the cosmetic barrel (which passes through a hole in the front of the grip, pinning the grip) and two screws at the rear.

The cosmetic barrel is a 6 inch piece of 5/8 inch stainless steel tube that I had left over from a previous project. To fit it into the tagger, I split the tube lengthwise for two inches or so, and clamped the split portion against the underside of the foreend U-channel sandwich. The clamp was improvised from a scrap piece of 1/16 inch sheet aluminum. I cut a small disk of ABS plastic with the simple expedient of heating the stainless tube over our gas stove for a few minutes, then pressing the heated end into a small scrap of plastic. Instant disk! Two small holes in the disk, two wires soldered to the LED (red for anode), the bare wires covered with heatshrink tubing, and I had a simple muzzle LED.

For safety reasons (it's my children that will be using this), I wanted to put a red muzzle brake on the casing. As far as I can tell, California law only requires it if the tagger will be sold, but it seems like a good idea if the police might accidentally come across a game in progress. I cut a length of fluorescent red acrylic rod, turned it to shape in the drill press, and polished the surfaces that I could reach. The brake fits over the cosmetic barrel, and catches the light of the muzzle LED nicely.

Paint and Finish

I wanted a "black rifle" look, at least for the primer coat. I'd decide later if I wanted a green or tan color, as seen on some of the XM8 photos, but I'd rather have those colors show black underneath if they chipped or flaked. I had a can of Gun Kote from previous projects, and had liked the results: a very durable matte black. As it turns out, Gun Kote now comes in other colors, including tan, olive drab, gray, and other camouflage colors. I may try one of those for the next project. Brownells have a number of other finishes, too, and some of those might be worth trying.

lower receiver, coated most metal coated 5 views left front view
The coated lower receiver assembly. Most of the metal done. 5 views of the finished tagger. The finished tagger.

I disassembled the casing (again) for painting. Each part got a few light coats of Gun Kote, as best as I could. The can was quite old, and it took a little work to get it working acceptably. I used a hair dryer between coats, and once the pieces were coated fully, I baked them in the oven as stated in the instructions on the can. The stuff smells terrible when baking, at least at first, probably as some of the solvents are cooked off.

I'd debated whether I wanted a wooden or plastic look for the stock. I finally decided on wood, and gave it a well-soaked Watco Danish Oil finish in Dark Walnut color. Danish Oil is a polymerized linseed oil finish; it soaks well into the wood, so the finish isn't compromised by scratches or dents. I wet-sanded the second coat with 600 grit wet-and-dry paper, which gives it a really smooth feel with a matte look. My only complaint is that it doesn't dry fast enough—my kids saw the dark stock and wanted to start playing with it immediately.

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