Missing fps in a gen9

Hi there,
I have a gen 9 m4 i have been working on for a while and no matter what i do i cant get its fps up.
Its running a 1.28 un balanced but it barely hits harder than a 1.18 in my mates gen8
I have done the seals and no matter what i do i cant get it past 240-270fps at best.
Its very air tight i even tried a sector delay to mix things up.
All i can think of is i swear the nozzle head is not coming out far enough upon firing,
I have taken it apart a few times now and everything looks fine and its shooting pretty straight too but it really should be hitting or exceeding 300 with its set up.
The nozzle head retracts a bit when it fires and i’m convinced it never goes all the way out again.

What inner barrel are you using? And Id size?
Also have you checked the t-piece for leaks? They can split easy and it’s not easy to see.

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standard 7.5mm inner barrel alloy tube. I dont think the t-piece is cracked its pretty new plus i epoxied the living heck out of all the edges.

The o ring is all good too, very strong compression pushing down, virtually no vacuum pulling up.

Is the nozzle stock or an upgrade? If it’s an upgrade, maybe check the o ring… and of course free movement on the cylinder head.
Sounds like you’ve got good compression, so if all that checks out, I’d be trying it out with a different nozzle… not much else it can be.:+1:

I block off two of the t-piece holes and I blow down the barrel. I just had an acr one leak and it had never been used.

If you tried a 7.3 barrel you would get a bit more FPS also length can make a difference too. Shorter lengths have lower FPS

go for M system, more reliable then the spring diameter system.
also spring length and material also play some part i suppose O_O

It really doesn’t matter if a t piece leaks like a sieve, it only has to seal between the nozzle rubber tip and the seat in the t piece.
The seams leaking mean nothing


i have not tried a 7.3, i find the outer diameter becomes a problem for gen 9s. I was sure shorter lengths gave better fps anyway and longer was more accurate. I know i can put bigger springs tighter bores in but it really should be hitting better with the current set up so i’m sure there is something i’m missing

i have a project p90 i want a good m spring for, but i modded my mates scar with just an alloy barrel, o ring and a 1.18 and his breaks 300fps no prob so a bigger spring i dont think is needed, i’m sure it will help but it seems inefficient to me

what would stop a nozzle going forwards all the way? if its not going forward enough i’m certain that would make a poor seal to the seat and drop fps badly.

BS there are just as many if not more crap M rated springs as there are GB dia. Rated springs…
Why is it that I don’t have one single M rated spring in any of my blasters? I have more springs than most stores have on the shelf :+1:


What brand do u recommend tho o.O?
SHS? Or?

SHS = :poop:
There are many very high quality M rated springs and many more that are complete trash, Availability is important and the really good M rated springs are not readily available in Australia and ordering good brand springs from HK , you will get a lot of fakes.
The springs that I currently use are the Ausgel springs, highest fps vs diam. and the most gentle on the running gear.
Efficiency is the key to success.

Here is a list of some of the best M rated springs available.


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It could. Look at nozzle seating area for any imperfections. Nozzle travel, measure it. Does it go far enough to make the seal to the barrel? Split the box, remove the springs and turn it over by hand to see if nozzle does what it’s gotta do.


yeh, when i get time time i’ll do that with some calipers maybe see if the tappet travel is being interfered with.
its possible since borrowing my mates chrono i have just become obsessed with measuring fps,
I have “chrono-virus” atm.

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Thing is I got relatives in taiwan, if I know what’s worth getting I can ask him so try source it there

I have some Laylax Prometheus springs on order to test, they are supposed to be one of the highest quality AS spring available.
These are Japanese made :+1:


i have gotten element springs to try. m135 the black coating rubbed off and went into the o’ring and little bits of black shit everywhere else. meh

why the hell would they put coating on constantly compressing part = .=?