FPS average and Dips.

[Standbystandby]

Hi peeps,

Before I ask this I will make it clear I am no gun tech!! I can change a hop and barrel etc... but I'm still finding parts all over the place of the first gear box in unscrewed! Anyway, today I decided to chronograph all my guns get an average and see what the biggest dip in FPS was. My tricked out G&P had a 330 average but dropped to 300 on two shots. My secondhand ICS shot 310 only dropped to 302 over 5 shots.

My question what would you guys say is an 'acceptable' drop in FPS? I have been airsofting a while now and I'm appreciating consistent FPS over high and inconsistent.

My next mission is to make all my gun as consistent a possible... the holy grail maybe!

Cheers

 

[Samurai]

Below 5fps is sniper category.

10 fps between lowest and highest is an OK AEG.

15+ is bad.

 

[Standbystandby]

Cheers Samurai, my G&P will fire 4/5 shots at 331 or 332 drop to 300 then come back up! It's strange!

 

[Jay85]

I run a Tippmann converted to HPA, I've done a fair amount of mods to it (TDC hop, orga wide bore barrel, heavy bolt, o-ring mod) over 10 shots my fps variance is no more that 5fps.

 

[Samurai]

Cheers Samurai, my G&P will fire 4/5 shots at 331 or 332 drop to 300 then come back up! It's strange!

You seem to have a problem with airseal. The piston O ring, nozzle O ring (if it has any) or nozzle-bucking misalignment problems are my first few ideas to check.

Or maybe the hopup unit can move forward too easily. Try putting a small piece of rubber between the hopup's "leg" and the upper.

 

[RR01]

How much time are you allowing between each chrono test shot? Each shot will raise the temperature of the components due to the heat created by compression of the air. It may be that after 5 or 6 shots in a fairly short time that the cylinder has expanded enough to allow a little air past the piston seal on the following shots. Try taking one shot every minute and see if you still get the same dip in FPS? If not, maybe think about putting a slightly fatter piston seal in there to take up the slack, as you will obviously be getting a drop in FPS each time you play and need to keep pulling the trigger on semi or auto.

If you still get a dip then if could be air leaking elsewhere, or as well as the piston seal, and will need investigating further.

 

[PT247]

Cheers Samurai, my G&P will fire 4/5 shots at 331 or 332 drop to 300 then come back up! It's strange!

Could be your spring, each shot will twist it slightly and if the end of the spring isn't flat then it could be notching on the spring guide, you could try a bearing spring guide which should stop it twisting so much.

 

[Standbystandby]

Cheers guys, great advice. Im going take it down to my local gun tech. He has pretty much said the same as you guys. When I did the work to it originally it sat at 330 to 335 consistently so I'm guessing something is now leaking or misaligned.... having retested it and leaving 1 minute between shots it did the same thing. I'll keep you posted.