Inconsistent FPS SRC M4

[Pew]

Hi,

Recently bought my first gun off here (second hand) and after having it chrono'd at the game the variation in FPS was huge, it would fire one or two shots at ~320fps and then drop to ~170fps and then return to 320fps.

Joe.

[G33m4N]

Re: Inconsistent FPS SRC M4

hello Pew,
i would look into the hop up as my first port of call, Torn rubber, misalined hop chamber, air leaks with different mag seating. things like that.

if all looking good up the front end, then its time to open the gearbox up and look for wear and tear on the piston head, nozzel and check all air seals.

[Mickydoos]

Re: Inconsistent FPS SRC M4

Some M4's have a little spring that sits on the barrel and psuhes the hop against the gearbox. Check if that is still there (not all M4's do so someone will need to confirm if yours is supposed to.)

[sigee]

Re: Inconsistent FPS SRC M4

I had a very similar problem.It turned out to be an air nozzle problem.
the nozzle wasnt always going all the way forward due to a combination of tight fit and weak nozzle spring.

[Pew]

Re: Inconsistent FPS SRC M4

Thanks for the replys, as I've never taken an AEG apart before are they all easy enough to check with no prior experience?

Joe.

[Mickydoos]

Re: Inconsistent FPS SRC M4

Disassembly of an M4 is relatively simple but I wouldn't recommend opening a gearbox till you've done some research on them. They're somewhere between fiddly and infuriating sometimes

[jakeno]

Re: Inconsistent FPS SRC M4

I have this same gun.
The gun does have a little spring at the front of the hop up, check for that.
The nozzle may be worn out, my old nozzle was a piece of cr*p so I got an shs aluminium one, works well.
There may be an airleak in the hop up is my first guess, check for the rubber, check for anything that may seem out of place. I recommend looking at online tutorials for V2 m4 fieldstripping, SRC have their own videos on their youtube channel which have take-downs of their own products, I advise you check them out.
If the gun is second hand, then there would definitely be some sort of airleak problem since I'm assuming most second hand guns have been neglected or just lots of use.
Opening the gearbox up really isn't as scary as people always assume, but for help if I were you, take pictures of the take-down so you know where all the little springs go. Also make sure the spring doesn't fly out because I had an m120 spring and bearing spring guide which just missed the window. So be careful.
I also dropped my gun on my foot. Don't do that.
It hurts.