GTA

All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: colorider on September 13, 2017, 07:17:07 PM

Title: Help with chrono numbers w my At44-10 New valve.
Post by: colorider on September 13, 2017, 07:17:07 PM

Long story short, I got a new tank for my at44 (22cal) and the new tank valve has a much stiffer valve spring than my original tank. It is causing some goofy numbers on the chrono. Old tank had a nice bell curve.  New tank starts off with much less fps than the original and the fps climbs and never comes down. Well, at least it didn't after 30 shots.! 
Pellet is the jsb 15.8gr. 
First shot was 809fps.   30th shot was 873fps.  Shots 2-29 were a really consistent steady climb up to the 873. 
Any suggestions how to make this curve, or rather slope more where it should be? 
Current setup is the hammer spring tension is 2 turns out, valve mod done so all but 1 is plugged. Perfect alignment with transfer port.
Filling the gun tank to 180bar. 

Thanks for any tips or tricks you can send my way.  I would like to have a more normal curve for accuracy.  A regulator is NOT of interest to me at this time. 
I have no problem adding more power to the spring for more fps, and no problem switching to the heavier JSB pellets if that would help.   I would like to get as much power as possible using the heaviest pellet as possible. 

Title: Re: Help with chrono numbers w my At44-10 New valve.
Post by: triggertreat on September 13, 2017, 07:42:58 PM

You should be able to increase the hammer energy to flatten out the curve better.  Usually you can do this by increasing the hammer spring tension which will offset the new stiffer valve spring.

Title: Re: Help with chrono numbers w my At44-10 New valve.
Post by: ackuric on September 13, 2017, 10:26:30 PM

+1, just add more spring until you get your initial velocity where you want it at, or reduce fill pressure until you're in that sweet spot! The bell curve is both pressure dependent and hammer weight/spring dependent, harmonize the two and you're golden! GL

-Matt

Title: Re: Help with chrono numbers w my At44-10 New valve.
Post by: Rallyshark on September 13, 2017, 10:36:24 PM

The easiest solution is to add a bit more hammer spring. If you wanted it to behave like your previous cylinder, and do it the hard way, then change out the valve spring for a lighter one.  The older cylinders had a much lighter spring, as you've discovered. I found that out myself way back when I got my bullboss, and later when I ordered a complete valve assembly.

Title: Re: Help with chrono numbers w my At44-10 New valve.
Post by: colorider on September 14, 2017, 01:37:22 AM

Thanks fellas.  Backed out the spring 1/2 turn and will see how it works out.