Low fps

[Spartan Steve]

Dropped my g&g cm18 recently had it on the chrono and it's now shooting at 250fps I've changed the spring, cylinder and cylinder head out of another combat machine still shoots at 250fps any one know what the issue could be?

[BrightCandle]

My guess is you have an airseal issue around the hop unit to the gearbox. When you drop the guns the barrels can shift or bend and at that point you can find the gearbox end of that with the hop unit can be misaligned.

[Sitting Duck]

yup - somewhere there it seems.....

is spring still on hop-up - is it "springy" pushing back to nozzle

with gun completely EMPTY on fire does barrel "bounce" or move slightly when fired

(absorbing & sealing nozzle into hop)

DON'T LOOK STRAIGHT AT BARREL BUT SLIGHTLY OFF - just incase a bb is stuck in there (eye protection doing this)

or flash hider or bent barrel restricting the innder barrel/hop "move & sealing" against hop-up/nozzle

(one flash hider I fitted once was too tight on inner barrel and was binding a bit on inner barrel

 

also check nozzle/tappet plate is moving and plenty of tension on it

 

how about - use the other CM top receiver & barrel and see if still way way under

 

if you done all you say then sounds like a nozzle/hop crap seal I think

even the paper test over mag hole don't always provide conclusive results if it is sealing but not quite 100%

 

deffo try another receiver/hop&barrel if poss to narrow it down a bit and save stripping down gearbox again

very easy to steam in and change this n that but often the ol' process of elimination is a wise thing to consider

(says the guy whose been there loads of times and will still keep arriving there no doubt)

[Spartan Steve]

Thanks for the advices guys think it's an issue with the spring on the hop up

[Sitting Duck]

swap some bits around to help narrow it down a bit

(lucky you got another CM16 to try stuff on)