G&G Green hop rubber are actually very good.
G&G Guns are known to have issues with ProWin Hop up chambers.
Like you i fitted one in my G&G TR4-18 (HK 416) and it worked like a beaut, installed one in an SAI G&P body and it worked well there too.
My friend wanted his upgraded too as he had a plastic hop chamber, so we put a ProWin hop in his G&G CM16 rifle and the performance was atrocious, every other shot was firing and inconsistent FPS. I discovered there was a significant air seal issue using the paper test. Went and bought a stock G&G metal hop chamber and all issues were solved.
As a tip, check and see if you have an air seal issue, looking at your pictures it looks like the air nozzle is not fully engaging into the hop chamber. This would mean that some or too much air is being lost out of the gap and that not enough air is going down the inner barrel to push BBs out.
To check you air nozzle to hop chamber air seal, cut a piece of paper into a small 1 x 1 cm square, ensure that your AEG is fully unloaded ie no BBs, plug in a battery so that the gun operates and place on Semi auto.
Turn the gun upside down so that you are looking down the magazine well and place the small aforementioned piece of paper over the hole where BBs would enter the hop up chamber and pull the trigger.
1 of 2 things will happen:
1: the piece of paper will not move or slightly move due to vibration, you have a good air seal
2: The piece of paper will fly out of the magazine well into the, you have a bad air seal.
If number 2 happens then it means that the ProWin hop will NOT work with your gun, get or use the stock G&G hop chamber because no amount of modding or bucking will help you AFAIK.
