Hybrid roller speargun build by DM Sea

Last Winter I started planning to build my first two hybrid spearguns (pictured below). I wanted these guns to be similar to a Daryl Wong hybrid only I wanted to use roller heads rather than standard muzzles. Having never built a hybrid I scoured through the spearfishing forums to research the topic until I had enough information to feel confident at taking a shot at it. After building 18 or so wood spearguns I was up for another challenge and looked forward to seeing it come together. After completing the guns I did some pool testing and had to adjust the bands several times before finding the happy medium between ease of loading and power. The guns work great and a few people have asked me to build one for them. This article will follow the build process on a new build started on August 9th 2016.

(My first two hybrid rollers built during the Spring of 2016)

1. Cut wood and carbon fiber tubing to size.

Wood being used is a solid piece of Afrormosia (two inches wide, three inches tall). The roll wrapped carbon tube has a one inch inside diameter and a one and one eighth inch outside diameter. Roller head by MVD

The total length of the speargun in this build is going to be 45 inches. I cut my pieces to the following measurements.

• Wooden stock 22.5 inches  
• CF Tube 28.5 inches

Eight inches of the CF tube will be inserted into the wooden stock, the roller muzzle adds an additional two inches making the total length 45 inches (one half wood, the other half CF tubing and roller muzzle).

I use a wet saw with a diamond blade to get a nice clean cut on the carbon tube. I also wrap the tube with masking tape on the cut line.

Now that I have the two main pieces of the gun sized correctly I will go about adding some layout lines to the stock. I want to mark where the mortise for the trigger mechanism will go and I also put a mark eight inches back from the front of the stock so I know how far to bore into the stock for the tube.

(I like to leave an inch of wood behind the mech.)

2. Cut pocket for trigger mechanism, route track and route hole for inserting the carbon tube.

This work will be done at the router table and it will be important to make sure all cuts are dead center. I used a cutoff from the stock to take some test cuts and get the fence on the router table set into position. 

(First I eyeball it with an 1/8" straight bit getting as close to my center mark as I can)


(then take a test cut and adjust the fence until it's dead center) 

Once the fence is set up I change the router bit to a 1/2 inch straight bit which is perfect for cutting the trigger pocket and the track which will double as a channel to allow the shank of the one and one eight inch ball end bit which will bore the hole for inserting the CF tube. 

(Woodworking 101; mark the beginning and end points of your bit so you know where to start and stop cutting on your workpiece.) 

(The two vertical lines on the workpiece show where the trigger pocket will be cut. These two lines are used in conjunction with the lines on the masking tape. This is a plunge cut so you can't see what is happening to your wood as you are cutting.)

The Neptonics reef mech I am using for this build requires a minimum of about one inch of depth if you want it to sit flush with the top of your stock. There is however a tab on the auto resetting version of the reef mech so I usually go another 1/4" or so deep for the front half of this pocket so it doesn't bind inside the pocket. I cut the pocket in four or five passes taking about 1/4" of material with each pass. After cutting the trigger pocket I use the same router bit to cut the track / channel for the ball end bit. I set the depth of cut to 5/8" and cut the track in three passes.

Now it's time to get out the big 11/8" ball end bit to make the hole for our barrel. As mentioned before this hole will penetrate eight inches into the stock. It's also important to mention the depth of this cut. I have calculated that I want the bottom of my tube sitting 1.6 inches from the top of my stock. This will give me enough stock above the tube to cut an enclosed track into the epoxy that will fill the previously cut channel.

(Setting the depth of cut)

(And there you have it!)

 

3. Square off trigger pocket, plug tubing, epoxy tubing into the stock and fill groove for track with epoxy.

The Neptonics Reef Mech has squared off ends so the mortise created withe the 1/2" straight bit needs to have it's ends squared off.

I use a 1/4" and a 1/2 chisel plus various rasps to take care of that task.

Before glueing the carbon barrel into the stock I like to plug both ends of the tube with rubber stoppers. I buy the stoppers slightly oversized and then adjust the fit using my belt or disc sander. I use wetsuit cement to help get the stoppers into the barrel and also to glue them into position. The rubber stopper at the muzzle end of the barrel gets pushed in about an inch and a half. This leaves some space between the muzzle and the stopper that can be filled with lead shot incase ballast is needed at the muzzle. The stopper at the other end of the gun gets pushed in only about half an inch. The space between the stopper and the end of the barrel will fill with epoxy as it is poured into the track.

I use west systems epoxy along with microfibers and graphite additive to secure the barrel into the stock. Everything is mixed in a paper cup which makes it easy to pour into the track because you can pinch the cup together and create a spout which gives a nice accurate pour.

Before mixing my epoxy I tape off the trigger mech pocket and the end of stock where the barrel is inserted. This prevents epoxy from running out all over the place.

 I rotate the barrel several times as I'm filling the track with epoxy to ensure the entire length and circumference of the tube gets covered with epoxy. 

The end result looks like this. 

After this initial batch of epoxy sets up and starts curing there will oftentimes be some settling  and maybe a void from an air bubble that needs to be filled in. If that happens I mix up another small batch to fill any voids and so the epoxy sits just slightly above the wood. I will let this epoxy cure for a few days before continuing. 

 

4. Route enclosed track and rout groove for the trigger on the underside of the gun.

After the epoxy cures for a few days I clean up the top of the stock by taking a very light cut (just enough so the wood is making contact with the blade, maybe 1/4 of the actual kerf) on the tablesaw. 

(after cleaning up on the tablesaw)

 

The next step is to route a channel in the track with a 1/4" straight bit. This groove will allow the shank of the ball-end bit to pass through and do it's job cutting the enclosed track. I set the router up to make a 1/4" deep groove and cut it in one pass.

Using the track that will be glued on to the carbon barrel later in the build I am able to set the correct height of my ball-end bit at the router table. It's super important to get this cut right because there isn't a lot of room for error.

I start with the bit up high then rest the track on the bit while lowering it until the bit is just touching the track.

Then go for the cut. When I make this cut I usually do about a third of the total length, then clean out the debris and repeat until I'm all the way at the other end. I find if I don't clean out the shavings things start to become difficult about half-way down the track,. Too much pressure is required to pass the stock over the bit while it's cutting.

After the track is cut I open up the first inch to inch and a half with the router bit you see in the above photo.

And the track is done!

The last thing I do related to the track is make sure the shark fins on the shaft sit high enough out of the track so the wishbones can be easily engaged. After loading the shaft into the track I noticed they were sitting a little too low, so I shaved a little more off the top of the stock. In the above photo you can see how much material was removed from the stock. The piece on the right is a cutoff from another gun I am building with the same wood.

Shark fins sitting proud above the track

Now that the track is cut my next order of business will be pinning the trigger mech into the stock but before this can be done I must route through the bottom of the stock so the trigger can poke through and move back and forth. A 1/4" straight bit on the router is what I use to make this hole.

 

 

The actual trigger is just a touch wider than 1/4" so i spend a bit of time with the rasps widening the hole so the trigger can move freely.

5. Pinning the mech and install the line release.

Once the hole for the tigger is complete I drop the mechanism into it's pocket load a shaft into the track and engage the mechanism. Then using a jig I mark off where one of the holes will be drilled.

Then it's over to the drill press where I'll drill only half way through the stock. Just enough so the bit goes into the pocket. The small piece of wood you see stuffed into the pocket is to prevent tear-out when the bit breaks through the wood.

 

After drilling this hole I put the mechanism back into the stock and check alignment of the hole by driving a pin into the stock. I have spare pins I use  that I've rounded the ends off of. The rounded ends make driving them into the mech easier if alignment is off by a hair.

If the pin goes into the mech OK I slide the jig over the pin. Leaving the shaft engaged in the mech I drill the second hole, again only half way through the stock.

Once the second hole is drilled I make sure alignment is good by driving the second pin into the stock.

Now I can finish the process by drilling through to the other side. I leave the mech in the pocket with one pin holding it in place as I drill each hole. I put masking tape on the side where the bit will be exiting the stock to again prevent tear-out.

Once both holes are drilled I do one final check to make sure everything is lining up.

These pliers are specially designed for grabbing ahold of pins and pulling them out of your stock which you will be doing quite a bit of during this process. 

The next step is routing the slot for the line release. I have some standard measurements that I use for this so all I need to do is get out my ruler and add some layout lines to the stock. I put the trigger mech into position on the side of the stock and create my first layout line. The line you see in the two photo's below will be used to set the fence to the correct position on the router table

The next part of the layout is going to be two marks needed for the position and length of the line-release slot.

Here I've marked the forward end of the slot

Once I have the layout done I make the slot by plunging in on the router table, the same way I did the mech pocket.

The resulting slot looks like this

Above you can see the tab that will be resting against the line release.

The next step is drilling the hole for the pin that will retain the line release. I have two measurements I use for this pin which is drilled from the top of the stock.

After finding the magic spot I make a mark with a punch and then it's over to the drill press to drill the hole.

After drilling the hole I pin the mech into the stock and then pin the line release into it's slot. If that goes well I load up a shaft to ensure nothing is binding up. If there is binding there a few ways you can fix that situation.

Fortunately everything lined up perfectly and I was able to pull the trigger, release the shaft and move the line release through its full range.

So far we have routed the track and mech pocket, glued in the barrel, noted the enclosed track, routed a slot for the trigger on the mech, pinned the mech and routed the slot for the line release. 

6. Route the recess for the handle base.

The technique I use for routing the handle recess is something I learned from the late great Gil Gacula. Gil was a top notch custom gun designer and builder who freely shared many of the techniques he used to build his guns. The setup is a little time consuming but the results are worth the effort. The recess is done on the router table using two fences and two stop blocks that limit how far the stock can be moved over the bit in each direction while cutting.

The first thing I do is determine placement of the handle (I am using a Neptonics AR-15 base and handle) and depth of the cut. I want to have the handle as high up into the blank as possible without having the screws that hold it in go up and into either the track or the carbon barrel. I will be placing the handle an inch behind where the carbon tube ends and I'll make a line showing how deep my track is so I can get an idea of how deep I can go.

The vertical pencil mark is showing where my carbon tube ends, the horizontal line (at the top) shows the depth of the epoxy track. Before going any further I decided to trim an inch of material off the bottom of my blank, it really doesn't need to be this tall and it will save me some extra work when I start creating this recess and later when I start shaping.

(the thinner blank with my the handle layout)

Once I have my layout all set up I take out my notes that tell me how to calculate the position of the two fences on the router table.

The primary fence needs to be 1.574 inches from the back of my router bit. I can get this fence into position pretty easily using my small 6" marking ruler and a piece of masking tape over the hole in my router fence where the dust collection is.

The auxilary fence has to be 2.9" from the main fence. To make this easy I cut two small pieces of scrap wood to that exact size and use them as spacers while clamping my aux. fence into position. These pics of wood will also be used as the stops I mentioned earlier which limit the travel of my workpiece on the router table.

The router table all set up (below photo)

 

As always, before cutting into the workpiece I'll do a test run on some scrap to make sure I have the recess centered on the blank, and also to make sure the dimensions are ok.

I did have to tweak the two fences slightly from their original position but it wasn't a big deal. Once that was done it was off to the races on my gun. The photo below shows the initial cut made with the 1/4" straight bit. The section in the middle is routed out before going any deeper.

The photo below shows the recess after completion.

It's deep! When the gun is complete much of that material will be gone and the handle will be sitting a recess to have it flush with the bottom of the gun. We'll get there eventually.

7. Route channel for pushrod, trim blank down, route recess for remote trigger, pin remote trigger.

The first thing I like to determine is how deep the pushrod channel needs to be. The AR-15 base I am using already has a channel in it so it really doesn't have to be that deep at all. I do have a lot of material to hog through because my handle is set high into the stock.

A quarter inch straight bit will cut the channel for the pushrod which is nothing more than 3/16" stainless round bar. The measurement you see in the photo below is how deep this channel will be inside the handle recess.

In about three passes, gradually raising the bit with each pass I have my pushrod channel.

The next task to attack is trimming down this blank a little more. I've put some marks on the blank too show how I want to do this.

I want to take off enough material so that my handle base will sit flush with the underside of the gun. The dark horizontal line (above) shows the maximum amount of material I can take off. I used a jig saw to cut into the stock taking away just enough material so I can make the long cut with my bandsaw.

Next I set up the fence on my bandsaw so it is about a 16th of an inch away from my line and made the cut.

The completed cut below

I use a belt sander to clean up this rough cut and do some preliminary shaping.

After the cleanup

Now I will start working towards installing the remote trigger which fires the gun via the pushrod. The first thing I do is mark the location and dimensions of this little pocket that I'll route using a 1/4" straight bit. Once I have those marks on the sides of my blank I like to determine the depth of the pocket. I play around with the trigger to see what I need so that the trigger can move front to back without making contact with the trigger guard.

Once I have all these measurements figured out I make the cut at the router table. 

Next I will test the fit by pushing the trigger down into the pocket and placing the handle over it moving it back and forth to make sure it's deep enough and not hitting the guard anywhere.

The trickiest part if this whole operation is getting the remote trigger pinned in the correct position. I use two measuring devices to figure out where the hole for the pin needs to be drilled. 

I use the depth measurement taken above in combination with my layout lines to determine where I will drill.

I then mark this spot with a punch and drill the hole (only through one side) with the drill press.

If everything goes well the hole lines up perfectly and the trigger still moves back and forth freely without hitting the trigger guard.

Success!

8. Trim the trigger on the Neptonics reef mech. Cut the pushrod material to length. Make a recess for the pushrod retainer.

The trigger on the Neptonics reef mech needs to be sized down so it doesn't poke through the bottom of the gun. 

Bolt cutters come in handy for this task.

It's an ugly cut...

a quick trip to the bench grinder and a minute with a file cleans it up.

It no longer sticks out the bottom of the stock.

I can now cut some 3/16" stainless round bar (the same material used for the pins that hold the mech and remote trigger in place) to length. I install the remote trigger and Neptonics reef mech so I can get a good measurement, mark the rod with a sharpie and cut the material with the bolt cutters.

After cutting I fine-tune the length with my bench grinder

Handle in place

Next I have to make a small recess for the pushrod retainer. I usually position the retainer around halfway between the end of the handle base and the trigger mech housing.

I cut the recess initially using a 3/8" foster bit with a hand held drill. The radius of the bit matches the curved ends of the retainer.

I place the retainer in position and then use a punch to mark where the drilling will take place.

I leave the pushrod in the cavity while drilling, to make sure I don't drill too deep. 

I will use a chisel and a rotary tool to adjust the shape to fit the retainer.

9. Devise a new way to secure the band at the bottom of the stock.

One improvement I wanted to make to the previous hybrid was the anchor point for the band. On the first two guns I used a 3/16" stainless pin that I bent in a hook shape. I epoxied it into the stock just in front of the reel. What I didn't like was how the band came down on an angle because the anchor was located an inch or so below the barrel. I felt it added extra drag to the barrel when tracking fish, it also was a little ugly. See photo below

Over the last few days I've been thinking a lot about how to improve this aspect of the gun so this morning I grabbed a cup of coffee and headed down to the shop with an idea in my head! A pin running through the stock, side to side with an access hole located at the end of the stock where you can feed a short piece of dyneema and tie off the bands. I started by laying out a mockup. 

I decided to use 1/8" stainless round bar for the pin. What I was aiming for was getting the pin as high up into the stock as possible without making contact with the carbon fiber tube. Also, having the pin located far enough back so there was a decent amount of wood in front of it for strength.

Once I had a basic layout I drilled the hole for the pin and using a foster but I drilled the access hole 

I roughed out a primitive shape and tied in some line. I think this is going to work!

Confident in my new design I started the layout on my new gun. I decided to move the pin back another 16th of an inch.

I drilled the hole for the pin first then I drilled the access hole. I set the depth on the drill press a touch above the carbon barrel because the fostner bit has a point on the end that I didn't want penetrating the carbon.

Access hole is in. I will remove some material from the front for the line  once I start shaping the stock. (After thinking about it this access hole r "slot" would have been super easy to do with a straight 1/2" router bit on the router table...next time)

10. Start shaping the gun

Now that all of the mechanical aspects of the gun are done I can move on to shaping. I start by creating some band grooves along the top of the stock. These should help the bands lay low once they are pulled back and the gun is loaded. A bearing guided cove bit is what I use, removing a very small amount of material with each pass.

After about 10 minutes of work this is what I got.

For rounding the bottom of the stock my favorite tools are a spokeshave and a rasp. These tools are very effective at removing material and don't create a lot of airborne dust which is a nice change of pace. 

Since a lot of my initial shaping is taking place at the front of the stock I like to tape off the carbon barrel with some masking tape to protect it from any accidental damage during the shaping process. Once I had the front rounded off a little I became obsessed with my new band anchor. I hogged out a nice channel with my rotary tool and the carbide bit you see in the photo.

 After a total of 3 hours or so using the spokeshave, rasp and sandpaper I have my final shape. 

Side-by-side shaped / unshaped

11. Drill holes for handle, push rod retainer and reel.

The last thing I need to do Is drill holes for the handle, pushrod retainer and reel. I drill oversized holes with a foster bit, fill them with epoxy and then screw into the hardened epoxy rather than the wood. The gun will be finished with an epoxy coating, using this method eliminates any possibility of water seeping into the wood.

I start out by marking where the holes for the handle will be drilled.

Then I measure the screw and figure out the maximum depth I can drill without coming up through the top of the gun.  

Using my ruler I least a ballpark idea of how deep my bit can go.

The top of the handle is showing roughly how deep the hole will be drilled. Looks good to me.

I use a hand drill to drill the holes.

Check the depth to make sure they are deep enough.

I follow a similar procedure for the pushrod retainer screw holes.

Next I'll mark The holes for the reel using the base for the reel.

I use threaded inserts instead of wood screws to secure the reel.

Getting an idea of how deep these holes need to be. 

 

I'll drill the holes so the insert can be set below flush of the stock.

After mixing up some West Systems epoxy with microfibers I fill each hole  using the paper cup method.

Holes are filled!

12. Fabricate a loading pad and countersink holes for pins.

On all of my past gun builds I have used big rubber stoppers sliced to half thickness for my butt/loading pad. I would cut them in half vertically with my bandsaw which was a total pain. Many times the stopper would get jammed, causing the blade to come off the wheels plus I always felt it was a little dangerous. I came across a thread on spearboard where someone was asking about what to use for a loading pad. One guy responded that he used acrylic plastic with rubber bonded to it. He would then use epoxy to secure the to the gun. He claimed that the plastic bonded better to the wood than rubber. I had been using epoxy and a single countersunk screw to secure my rubber stopper which had worked well but I was never 100% happy about having the screw on there. So I figured I'd give this method a try. I liked the pictures he had posted of the end result.

I purchased the rubber material on Amazon and I found the plastic on eBay. I've always used 5 minute epoxy for this task.

I started buy tracing the butt end of the gun onto the plastic then I cut out an oversized square with my bandsaw.

I then used the plastic square to size the piece of rubber also to be cut with the bandsaw.

Once I had my two pieces I applied my epoxy and put them in a vise to hold them together. I let the epoxy cure for almost 24 hours.

A day later I came back and I had my plastic and rubber bonded together.

After taping off the bottom of the gun I applied epoxy to the butt end of the gun and the plastic. I then stood the gun up and applied slight downward pressure while securing the barrel in a vise.

I left the gun standing for 24 hours before shaping the pad. I beefed up the masking tape with a layer of duct tape because I didn't want my belt sander (used for shaping) hitting the wood during the shaping process.  

During shaping unfortunately, the rubber separated from the plastic. I was about 3/4 of the way finished shaping the pad when it happened. After peeling the cured epoxy off the rubber (it came ff in one solid piece) I had to think about how to fix it. The plastic was really slick, so I decided to scuff it up with sandpaper hoping the epoxy might adhere better. I did the same to the rubber pad. I also decided to go back and add a countersunk screw just in case at some point the epoxy decides to come undone. Finally I added some microfibers to my epoxy mixture to help with the bonding. I again let everything cure for 24 hours before finishing with the shaping.

Here is the final product. It came out pretty nice!

One last thing I wanted to do was countersink all the various holes that were drilled to accommodate the stainless pins that will hold the hardware in place. I used my rotary tool with a cone shaped bit to do this.

The result.

Next up I will be painting three or four layers of Phils Epoxy on the stock to make it waterproof. Below is the gun after sanding to 220 with a random orbital sander.

13. Painting with 2 part epoxy

After sanding to 220 with a ROS I use an air gun to to remove and dust left behind from sanding. Before painting on any epoxy I also wipe the wood down with acetone on to remove any contaminates (grease, oils) that could be on the wood. I then move out of the dusty confines of my basement shop to a small heated room in my garage where there is much less dust.

Supplies needed for this process: Epoxy, nylon bristle throwaway paint brushes (inch to inch and a half size). Small scale for measuring/weighing epoxy, mixing cups, tongue depressors to stir, pipe cleaners, dye.

I took care of coating the inside of the mech pocket, handle recess and all the holes for the pins before sanding so I wouldn't have to worry about sealing those areas during finishing.

I started by painting on two very thin coats of tinted (blue) epoxy waiting roughly a day between coats. below is what it looks like so far, side by side to it's unfinished twin.

Before doing another coat I will sand this down with 400 to remove any imperfections (bumps, orange peel etc...).

Below are my sanding supplies. The epoxy is still chemically active so I like to wear gloves to avoid contact with the dust and also a dust mask to avoid breathing it in. I sand on top of an carpet floor mat to avoid gouging the epoxy which is prone to scratching at this point.

After sanding I blow the dust off with an air gun and give another wipe down with acetone.

After painting another coat on my gun I hang it from the barrel as it cures.

I'll apply one or two more coats depending on how it looks. My goal is to have as few imperfections as possible.  Once I'm happy with how the gun looks I will wait a week to let the epoxy harden before I start assembly.

14. Final Assembly.

After letting the fourth coat of epoxy cure for 6 days I am ready to start the process of assembling the gun. Assembly can be an adventure sometimes because epoxy build-up and drips can cause problems when it comes time to install pins, the mech, the trigger etc. If parts don't fit correctly you have to get out a file or rotary tool to shave down the epoxy that is preventing the part form being installed. You have to be careful when installing pins because epoxy that inadvertently  drips into a hole can cause wood to split when hammering a pin through the stock. Not fun after spending hours and hours working on a gun! I've learned to oversize the mech pocket, trigger pocket and handle recess slightly to ensure everything fits without having to spend extra time making adjustments after the epoxy has been applied. 

Before I start putting the gun together I like to buff out the shine (what some people refer to as the "Glass" look) from the epoxy so the wood has more of a natural look. I start by lightly going over the entire stock with a Scotch-Brite pad and then do a final buff with Meguires #49 Oxidation Remover.

Above you can see the shine coming off the bottom of the stock. Below you can see the finish after the buffing treatment.

The first part I like to install in the gun is the trigger mechanism. The mech is held in with two 3/16"stainless pins. Sometimes the pins included with the mech need to be shortened because they poke out the side of the stock. I use a bench grinder to grind them down if that is the case. Other times the pins can be too short which is why I always have a few lengths of the 3/16" and 1/8" stainless on hand. The 3/16" stainless is also what is used for the push-rod. If I find the pins are too short I cut new ones and adjust for a perfect fit with a bench grinder.

Before putting the mech into the pocket I first take the modified pin with the rounded end that I was using earlier in the tutorial, put a dab of silicone grease on the end and carefully drive it half way into the stock. I then pull the pin out and do the same thing on the opposite side of the gun. I do this to help prevent any splitting that might occur If I were to drive a pin with a square end all the way through the stock in one go. I have had that happen because epoxy built up near the outside of the pin hole and the epoxy was stronger than the wood. As I was driving the pin through the pin caught the epoxy and the wood chipped out. Ugly.

Below, tools for installing your pins

The mech installed beautiflly without having to make any adjustments and with no mishaps while driving the pins through the stock!

The pin included with the line release is going to be too short for this gun so I will have to make one the correct size.

After cutting the material to the approximate length I fine-tune the length on my bench grinder. To install I follow the same procedure previously explained.

The next pin I need of the same 1/8" material is for the band anchor. I measure cut and grind same as before.

After fine-tuning the fit, looks good!

Next I will install the remote trigger by pinning it inside it's pocket. 

Now I can install the pushrod and pushrod retainer.

The holes for the retainer need to be drilled into the epoxy filled oversized holes that were drilled before the epoxy finish was applied. Once the holes are drilled It's a quick and easy installation

 

Up next is installing the AR15 handle base. I start by drilling some pilot holes into the epoxy

Next I want to get an idea of how deep I need to drill for the screws that will hold the handle in place. I mark my drill bit with a piece of tape.

Once the holes are drilled it's just a matter of installing the screws.

It's starting to look more and more like a speargun!

The next item to be installed is the base for the reel. I will be using the threaded inserts in the photo below. I start by drilling a pilot hole into the epoxy with a small drill bit followed by a larger bit. 

Once I have my holes drilled I take my rotary tool to put a subtle countersink into the epoxy. This helps when installing the inserts which have the tendency to wobble slightly when trying to get them to bite into the material. 

The screws that thread into the inserts are used to install the insert.

Once both inserts are installed the reel base is secured by the two machine screws

The last two pieces of hardware that have to be attached to the gun are the track (rail) that sits on the barrel and the roller muzzle. The plastic track (made by JBL) has an adhesive strip on it so installation is simple; clean the barrel with isopropyl alcohol, peel off the backing and press into place. I do just that after making some marks on the barrel to use as a reference. I load the shaft with the track sitting on top of the barrel and use a few pieces of masking tape to mark where the edge of the track should sit when I press it into place. I also needed to cut the track to the correct length before installing.

After installing the track I push the roller muzzle into the barrel and drill a hole through the barrel and into the muzzle. A simple stainless screw will hold the muzzle in place.

Muzzle and track installed

15. Rigging the gun!

Now that the gun is all put together it's time to make bands, attach a shooting line to the shaft and load the reel up with some line.

I'll start by making the bands. This is only my third roller build so getting the bands fine tuned is a bit of a process. I'll cut some material to ballpark length but most likely I'll be adjusting them (making them shorter) slightly after initial installation. I'm using Salvimar "Z-Boost" rubber which can be stretched further than standard band material. This means I can use shorter bands which will deliver more power.

Before making the bridle and wishbones I will taper the ends of the bands using my bench grinder. Below is the result. It takes less than a minute per band.

Now I will use some Dyneema line to make the bridle that will facilitate stretching the band back and the wishbone that engages the shark fin on the shaft. I cut two pieces, one longer than the other. A simple overhand knot on each end is tied and then inserted into the end of the rubber.

Below you see the bands, completed bridle, loops for the other end of the bands and various tools used to assemble the bands. 

Before trying to insert the ends of the bridle and loops into the small hole at the end of the band I take an awl with a dab of silicone grease on it and lubricate the opening of the hole.

After installing the bridle / wishbone with the "T" shaped installation tool (two photos above) I use special cord to tie constrictor knots. This kevlar cord bites down on the rubber and keeps the knots from pulling out. 

After tying the first constrictor knot I pull it tight and tie another one on the opposite side of the band.

Below, after both ends of the bridle are tied into the band. 

In the opposite end of the band there is a loop, with a special knot that is formed with an additional piece of line that is looped through the band anchor. The photo below illustrates the knot.

And below here shows both ends of the band tied into the anchor.

The gun now has a power source!

All that's left to do now is to hook up the shooting line to the shaft. I'm using 200LB test monofilament line and it will be crimped to one of the shark fin tabs on the shaft. Below you see the basic tools and supplies needed; Crimping tool, crimps pigtail swivel and in the upper left and bottom left corner hi-viz mono.

After threading a crimp on the mono I loop it through the shark fin and then the other side of the crimp.  Then I burn the end so a ball forms which will prevent the line from sliding out should the crimp fail.

I start by crimping in the center and then once on each end being carful not to crimp down over the end of the metal and digging into the line.

After loading the reel up with some spectra spearfishing line I connect a pigtail swivel to the line with a bowline knot. There is a loop (held in place with a crimp) on the other end of the mono shooting line which is then attached to the pigtail. This setup gives you an easy way to disconnect the shaft from the gun should the need arise.

After connecting this pigtail to the shooting line there's nothing left to do in the shop except take one final picture.

Then a photo session down at the beach.

Video link of some test shooting