Step 1. Read the DIY Roller Speargun instructions before you start. Yes, all the way through!

Step 2. Remove the screw holding the original muzzle. It may be corroded in so you may need to use penetrating lubricant. Mine was so tight I had to use a block of timber and a hammer to tap it out.

Step 3. Mark the barrel for the required length reduction. Skip this if you’re not changing the barrel length.

Step 4. Cut the barrel to the required length. It is important to make sure the cut is square to the barrel so the power head fits properly. If using a drop saw make sure to use an aluminium blade. Otherwise a hacksaw will do the trick.

Step 5. Sand the inside of the barrel to remove any oxidation or foreign matter to ensure a good seal. It is also important to file any sharp edges to prevent damaging the plug’s “O”rings upon insertion. Filing the outside edge of the cut will prevent any annoying sharp edges.

Step 6. Lubricate the inside of the barrel and the power head plug with marine grease before installing into the barrel.

Step 7. Use a twisting motion to insert the the Roller Power Head into the barrel. Twisting will prevent damage to the “O” rings and ensure a good seal.

Step 8. Align the Roller Power head with the rail. I used the spear in the trigger mechanism to make sure everything was aligned. The power head may sit proud of the rail but this will not affect accuracy or flight path.

Step 9. Turn the gun over and measure 8mm back from the conversion plug. Mark the hole and use a centre punch to get started.

Step 10. Drill the 3mm hole.

Step11. Screw in the provided screw and the muzzle is fixed into place.

Step 12. Remove the screws either side of the handle and and drill out the holes with a 5mm drill bit to accommodate the new handle-pin and anchor bushes.

Step 13. Drill out the screw holes with a 5mm drill bit for the new threaded handle pin. This pin will hold the line anchor bushes.

Step 12. Put one of the line anchor bushes on the threaded handle pin then push the pin through the handle. Next put the other line anchor bush on and tighten the nut with and 8mm spanner. Cut the remaining handle pin off  flush with a saw and file smooth.

Handle pin and line anchors in place and your DIY roller speargun is done.

The front end of the DIY Roller Speargun with Manny Sub Roller Power Head installed rigged and ready to go.