Drop-In Rotary Hop-Up unit for the G&G F2000 AEG.

Been working on this one for a while! The stock F2000 hop unit, while good, is a monster to adjust on-field, especially with gloves on.

You will be re-using your hop-up body spring, barrel clip, barrel centering ring, barrel O-ring, and the cross-pin for the hop arm off the original hop unit.

The additional hardware you'll need is 1x JIS 1.8x12 (or US #013) O-Ring, a 1mm ID 1mm CS O-Ring (green gas fill o-ring), and a M2.5x8mm flat or cup point grub screw.

The body of the hop-up unit is not printable via FDM processes. You will need either SLA, SLS, or other similar processes (MJF, DMLS, etc) to create this part successfully. I also recommend printing the knob in FDM or SLS, as grinding SLA on SLA will rapidly wear the parts.

If you're trying to sneak this by one of the cheap SLS outfits, rename the STL's to something unreleated like "soap valve" or "toothbrush clip".

- Printing -
The body of the hop-up has 2 versions - One for SLA printing, the other for SLS. The SLA part has a 0.5mm fillet in the barrel clip corners to prevent stress cracks. You will need to file your barrel clip corners slightly to clear these fillets. The SLA part also has printed-in threads, as SLA prints tend to crack.

SLA prints should be in an ABS-Like, tough resin.

The hop arm should be printed in whatever format you use for the body, but the knob can be FDM, SLS, SLA, anything. The only thing that should only be FDM or SLS is the assembly clip, as it needs to have flexibility.

- Assembly Instructions -

1. Run the appropriate drill & tap for M2.5 through the hole in the hop arm bulkhead parallel to the barrel, where you'd expect the stub for the hopup spring to be. On SLA parts, be sure to align the tap with the existing thread start before chasing the printed threads out. Install the M2.5x8mm grub screw till it's flush with the inside wall.

2. Slip your hopup spring over the grub screw and secure with a drop or two of super glue if needed.

3. Install a JIS 1.8x12 O-Ring on the body grooves closest to the feed tower.

4. Install your barrel with bucking, brass centering ring, and retainer o-ring. Clip in the barrel clip afterwards.

5. Place your nub of choice into the nub pocket, then place the hop arm on top. Install by pressing the crosspin salvaged from the original hop unit through the holes in both parts. Secure with a dry 1x1mm o-ring to keep it from slipping out. If the cross-hole has shrunk in printing, use a 2mm (or Wire Gauge 46) drill bit to open the hole back up to size.

6. Install the hopup knob, pressing it over the o-ring. Make sure to line up the flat tail of the hop arm with the cam groove in the knob. Secure in place with the assembly clip in the exposed grooves behind it.

7. Reinstall the hop-up into your AEG and test!

- Parts Notes -
If you are missing the spring, McMaster 9657K628 is a drop-in replacement. The crosspin can be replaced by McMaster 90270A222 if you grind the threads off. Or not, I'm not your dad.

- Amazon Parts Links -
JIS 1.8x12 or US #013 O-Ring: https://a.co/d/ig9jQFA
1x1 O-Ring: https://a.co/d/1s8gCJ0

- Troubleshooting -

1. If you are using a tapered-lip bucking (ex. Maple Leaf Macaron) and not a straight-lip (ex. Prometheus Purple) you may find that the BB's won't pass the bucking lips without a bunch of force. This may require you to pass a 7.3-7.4mm or Letter L drill bit through the bore of the hop unit, as the diameter shrunk during printing. The model is 7.4mm and will still work down to about 7.3mm.

- Update - 9/22/2024 -
Added a new set of hopup arms to fine tune hopup pressure - I found that with the hopup maxed out, I could not overhop a 0.28g BB when using a 75deg Macaron bucking and Omega nub. The +0mm is the same as before, with a circle through the arm. +0mm Alternate has a hexagon through it, and moves the nub contact out 0.5mm for better centering. +0.5mm moves out and up 0.5mm for more contact pressure, with a square through the body. +1mm moves out 0.5mm and up 1mm for even more contact pressure, with a triangle through the body.

- Update - 10/26/2024 -
Tested the +0.5mm arm this weekend, and now the hop unit acts exactly like every other Hop-Up unit I've ever used, hopping 0.28g BB's with a little less than half the total range on the hop wheel.