Varying FPS?

[Indieboi918]

3 Weeks ago I took my gun to an Airsoft shop and had it chrono'd it came out at about 340FPS

2 Weeks ago I took it to my site for it's first game and it chrono'd at about 335FPS at the site.

Today I took it back to the same site to play again... the first shot was at 351 FPS (only 1 over the limit) 2nd shot was at 360, the highest I'd ever seen this gun chrono, so I had to hire a gun for the day.

what I want to know is how is it possible for the gun to be at 335 and then 2 weeks later be at 360?

Looks like i'll be getting a weaker spring.

Thanks,

Steve

 

[JerseyRider]

What make is it?

 

[Indieboi918]

<<< KWA it's a KG36C

 

[Deva]

How many rounds have you put through it? Also did they have a different chrono at the site? I wouldn't like to think different chrono's would vary that much but I guess you never know..

 

[B00ts]

yeah chronos vary alot,

different makes different tolerences

 

[Indieboi918]

It's a pretty new gun so only about 2-3 470 round hicaps & i'm not too sure if they used a different chrono at the site, didn't pay much attention to it but it looked pretty much the same (bright blue all over).

 

[Hubert]

It is actually possible that it is the gun, and not the chrono.

There is a reason why G&G put a spring release on their L85 series (and now their newer G&G FN F2000 series).

The piston in a gun has numerous positions. These change everytime the gun fires, as the gearbox cycles - and vary from compact and in, all the way to fully out. If you finish firing the gun whilst it is at the compact position - it will keep the spring in the compressed.

The next time you fire the gun (days/weeks/months) - if you haven't fired the gun since the last time - the FPS will have changed. (I found that it usually goes up if the spring is compressed) The longer the spring is compressed, the higher the FPS can become (This is from my experiences - others may differ)

The spring release on G&G models allows the piston to move to its loosest setting, allowing the spring to extend to an uncompressed length. This keeps pressure off.

For those guns without a spring release (i.e. practically all of them) there is a way to solve this (where the piston and spring are) however, I cannot remember what it is - I think it is shooting until the spring is at the correct setting.

Another reason relating to the gun (I've only ever seen this on the Army Armaments R85, so could only be related to that) is that the way the gearbox cycles could be doing it. My old R85's chrono'ing was always a laugh (when it worked fine) in that few readings were ever the same. The gearbox would start at a low FPS (lowest 295) and slowly rise up to about 370 fps - then drop back down to the low 295-300fps, and slowly rise back up to 370. This cycle woudld take about 15 shots.

Again, it could be the chrono. My old R85 once registered as 0000fps, 275, 0001, 366, 0024, 4267 (around twice that of the real L85) and finally 345fps.

 

[B00ts]

Sounds like the gun has bedded in and loosen up which is why its increased fps .

i've had guns change change fps from week to week without anything being done to it .

Instead of changing the spring try leaving the gun in the cocked postion( spring compressed) for a few days to a week ,this should bring the fps down abit .

As you can't see the spring without taking the gun apart look in the mag well at the hop up and your see the nozzle move backwards and forwards when the nozzle is in the open postion the spring should be compressed it may take a few shots to get it that way .

 

[Indieboi918]

Looked inside my magwell and fired a few shot but saw no movement at all, so I guess my gun is slightly different.

 

[kejot]

also do you know what bb's were used each time?? a lower weight will give you a higher fps

 

[Indieboi918]

Yeah I used the same make of .20g BBs in each chrono

 

[JerseyRider]

Looked inside my magwell and fired a few shot but saw no movement at all, so I guess my gun is slightly different.

You wont be able to see anymoving comming from the magwell becuase the gearbox is behind the magwell and in frount of the stock

Even if you could see the gearbox trying to see the spring is a differnt problem all together

 

[B00ts]

The air nozzle travels backwards and forwards within the hop-up unit it what loads the next bb and is be visible while looking in from the magwell.

you may need a torch