Silly low fps issue with SHS/Rocket nozzle in G&G CM16 SRS

[SmaSim]

I've put a new spring in my CM16 SRS so while I was taking the gearbox apart I changed the Piston Head and Nozzle with O ring, both being Rocket parts based on reading the forum (identical to SHS parts as described). The upgrade spring was because I was getting just under 280fps.

Nozzle used;

https://www.ak2m4.co.uk/internal-parts/air-nozzles/ra-m4-aluminium-nozzle

I put it all back together and chrono'd and got a very low fps of 130 ish.  Took it apart and couldn't see anything obvious, checked the seal on the nozzle by pushing the cylinder in and all good, no leaking. The O ring was freely moving the length of the nozzle and had been lubed. I only did this unextended (didn't think about extended until reassembled).  Reassembled, and no good again, same poor result.

Stripped down, put the original G&G nozzle back on - which doesn't have a good seal (no O ring) - reassembled and tested. Good news 330fps.

The length of both nozzles is the same (checked with micrometer) and the only noticeable difference is there is a bigger chamfer on the end which meets the hop. I can only guess this is where I lose pressure?

Help! Any thoughts on why this new nozzle didn't work? Anyone found the same?, advice in the forums points to these nozzles.  AEG is only 6 months old to give an idea on V2  gearbox spec.

If the G&G nozzle is leaking with the original spring my thought is that with better nozzle (and original spring) I'll get higher fps and lower stress on the gearbox, surely better all round.

 

[Sitting Duck]

Have you got a spring on hop unit ???

basically the spring ensures the hop is pushed fully back against box to seal better

Often if you plug in a mag it "can" bring the hop away from gearbox and result in light contact

in this instance light contact means under pressure the lips of the bucking where nozzle seals

well it can blow under pressure and there is ya drop in fps

Yes the SHS nozzles are usually correct for G&G's

but G&G's have that round chunk on the side but they don't always fit a tiny spring on hop unit

rip apart an old clicky bic pen or something and polop it on the hop unit's lug/nipple (snigger)

Ahem....

or a larger spring just the exact size over the barrel

or a couple of o-rings (not springy) to force back the hop unit in place

Next time it might be wise to light sand the front of tappet plate (on a table in circular motion)

to help the nozzle return a whisker more foward to seal on bucking perhaps

reckon you might get the thing to seal up if the hop sits back in place ok

There are other factors,

on some very new G&G hops the red SHS nozzle can be a whisker too snug/tight fit

(think you should be ok though after 6 months)

or

if the box has been fitted poorly the box can tilt upwards slightly and nozzle can scrape inside hop

(basically restricting the nozzle sealing perfectly asap in use)

most likely the hop isn't being held back against the front of gearbox with a spring

some guns need it more than others

G&G sometimes fit a spring - sometimes they don't

Just like they usually use bronzey bushings but others they use bearings

Also they may use phillips or wtf hex bolts on the gearbox to be ar$ey

(jeez I wish they get their consistency sorted)

 

[SmaSim]

thanks for the feedback, the hop has no spring fitted, it's gray but like to top one. 

What doesn't make sense to my little noddle is that the original G&G nozzle is the same length as the SHS with a worse seal but give high fps. I'd need to take photos but from memory the G&G nozzle end is more radius and the cyl dia goes closer to the end compared with than the chamfer on the SHS.

I need to have a look at how the SHS mates with the bucking. As you say pushing the hop back a bit might make the fit snug and reduce/eliminate the loss there, one experiment to make.... Maybe the G&G is snug enough by chance. 

Worst bit about the box is the screw on the 'wrong' side, why?!

 

[Shizbazki]

I know that G&G nozzles and hop up units are notorious in this aspect in that they have to be G&G ones.

I once installed a ProWin hop up unit in a mates gun becuase he broken the hop up unit and the FPS dropped by a huge amount, checking the air seal showed that they was no seal between the hop up and air nozzle. Installed another G&G hop up unit and perfect air seal.

To check the Air seal assemble the gun fully, turn it upside down, ensure there is no BB in the gun, plug a battery into the gun as normal and place a piece of paper about 1cm by 1cm over the hole where BBs would feed and pull the trigger.

Should you have a good airseal the paper will only move a little or drop off the side of the feed hole.

If the paper should come flying out the magwell then you have a bad air seal.

I'll be honest the G&G air nozzles are fine without the rubber o-ring, if you have used good silicone grease on the Cylinder head nozzle you should have no seal problems there.

My G&G TR4-18 ran at 341FPS +/-1 FPS using .20g BBs with the original air nozzle installed.

 

[jcheeseright]

Surely the easy solution here is to just put the G&G nozzle back on? If a part reduces the performance of the gun it’s not an upgrade!