HPA is Wacky

[SqueegeeKid]

I just recently bought a brand new PMI 88ci 4500 preset tank to put on my SmartMag. Before i was using CO2.

I went to my local field for a test drive with my new system and went straight to the chrony. I was not impressed with the results.
The FPS was going anywhere from 207 to 250. I upped the velocity and it was doing the same thing. With CO2 it was pretty consistent (+-5fps on average)

Is there something that might be wrong with my gun or tank? The parts inside my gun are at least 2 years old. Don't really know how old since it was bought used.


I know thats a pretty vague description of my problem, hopefully someone can give me some things to look for/replace.

[FrAuStY]

I'm not sure if that gun was shipped with the HPA piston or not, and since you don't know how old it is.. you'd prolly wanna call agd (to find age). I know that previous to widespread use of HPA the guns had a stiffer spring for the CO2. I know they're like 20$ for the HPA piston. Before you buy that though.. get an AGD rebuild kit and re-O-ring it all. Could also be a bad reg seat. Does the gun work right with CO2 after you've tried with HPA? If it does it sounds like maybe you got the wrong piston. If it doesn't work right at all check reg seat.

Peace

[SqueegeeKid]

It worked perfect the last time i used CO2. Unless hooking HPA up to it messed my gun up, i bet its the piston. This gun is pretty old.

[MikeCouves]

Yeah that's what I would say it is. Get a HPA piston and try that out, and report back.

[Cristobal]

Just curious, what is a HPA piston? Is it a replacement regulator piston? But how would that help, and where do the stiffer springs come into play?

[MagNumPI]

Yeah i would like some info on that too. And are they free or what?

[FrAuStY]

I don't know much about it..as mine was shipped ready-to-go with HPA. If yours is an older one and has always been shooting on CO2 it may not have the new piston. (I really don't know what all needs to be replaced i.e. spring pack and piston or just the piston.) You may want to call AGD and they should be able to tell you what piston you have via the serial no. on the valve. I heard that before HPA was widely used.. the guns came with a piston designed for the fluctuating pressure of CO2. I'm not a know-it-all so you may want to call the experts.. AGD it could be something else. Here's a link to the piston :
HPA piston replacement (http://store.airgun.com/acb/showdetl.cfm?&DID=17&Product_ID=48&CATID=6)

:D

[SqueegeeKid]

I just got off the phone with AGD, said it was my reg piston. They're sending me a new one and a bunch of extra o-rings and stuff. Rocking.
Ordered an intelliframe while i was at it. Woohoo!!