Tools required for installation:
- drilling apparatus (drill press is preferable, but hand-held drill will also work)
- 3.5 mm drill bit
0. Disassemble everything
Take apart your gun and disassemble the hop-up unit. That includes removing the black hop-up adjustment parts, spring and plunger for it, hop-up arm and taking the metal shell apart. Keep just the inner barrel, bucking and hop-up shell with fasteners. You can store the rest of the parts for safe-keeping.
1. Prepare the drill jigs
Take the hop-up chamber shells and screw them together without the inner barrel and bucking installed. Then insert them inside the outer barrel and align the mag-well hole.
Then take the larger drill jig part and push it on the outer barrel. Align the screw hole with the hop-up chamber hole. Use the M3 screw from the mag-well to secure the drill jig in place.
Take note of the orientation! Arrow should be pointing the shooting direction and the circle should be closer to receiver end of the barrel.
2. Drilling the holes
Check the position where you will be drilling the hole! If the hole is exactly on the edge of one of the flutes, it is strongly recommended to use a drill press and use the jig just as a guide.
Hole doesn't need to be 100% precise and in worst case scenario, you can drill a larger hole to account for some imperfection. In most cases, 3.5 mm is totally enough.
Option A: If you have a drill press, you can use the flat sides of the jig to clamp the barrel securely in a vise. Use a 3.5 mm drill bit to make the hole.
Option B: If you don't have a drill press or vise available, don't worry. You can use the smaller piece to lay the barrel straight on a flat surface. Use a 3.5 mm drill bit to make the hole. Just make sure to drill as straight as possible.
3. Remove the jigs
Remove the drill jigs from the outer barrel and take out the hop-up chamber. Inspect the hole and remove some sharp edges if needed.
4. Assemble the hop-up chamber
Choose whichever hop-up arm you like - A is flat and B is slightly concave. There is no definite better design - use whichever you believe is better. Both arms will work perfectly with r-hop and stock bucking.
Assemble the hop-up chamber with the hop-up arm, the inner barrel and bucking.
5. Install the screw
You can now install the hop-up assembly back in the outer barrel. Align the mag-well screw and install the screw of your choice - thumbscrew or grub screw (uses a 1.5 mm allen key).
Install the screw and check the hop-up chamber with your eye while looking through the barrel at a light background. At one point you should start seeing the hop being applied.
And you're done! Reassemble the gun and you are ready to rock!
Optionally you can take a permanent marker and paint the inside of the hole to make it less shiny: