Bullgear CNC Machined Hop-Up for Airsoft AEG Machine Gun
(Model: G&P Stoner MK63)

"This is the only Hop-Up you should every be running in an A&K or Classic Army M249. If you have one of the M249's this is made for, buy this up while it's still in stock. This hop-up unit completely eliminates all the issues with the stock units. It feeds flawlessly and when installed correctly with quality parts (bucking, Barrel, ect.) allows for extremely consistence shots.

"Works a treat and nicely fixes the weird feeding the stock hop is prone to on an A&K M249.

I got a Gen3, which uses four screws to hold everything in place.

Bullgear recommends a purple Prometheus bucking - do what they tell you. I tried doing some thinking (Mistake #1) and using a Red, since my gun is running ~390fps. Big mistake - doesn't work.

Put in a purple? Needs less than half the adjustment range to hop 0.28's.

Great hop unit - just make sure to listen to Bullgear and use the right bucking!

"i have the gen 2 version of this (has two screws to pull the barrel clip up, and a screw for the hop up arm not a lever) and i have been very pleased. Truly a drop in mod to correct the hop up issue from A&K. I did have to run a slightly longer nozzle to achieve full compression but not a huge issue, for me 21.6mm was the correct nozzle length and i put a slight chamfer on the end of mine. checking against my chrono (acetech5000) im getting deviations of about /- 2fps @23 rps which is great for me. This is in a MK2 with a 510mm barrel.