Can an increase in FPS be guesstimated by change in regulator ?

[grumpy]

Wondering if an increase in fps can be made by changing the regulator on my 2240 HPA project.

Right now its got a 3000 psi, 13 ci tank thats regulated at 800 psi. Its shooting between 597-601 fps

I was curious if an estimation can be made if I were to move up to say an 900 or 1000 psi regulator.

Thanks
Dave

[rsterne]

Here is a graph of testing I did with HPA on a stock 22XX valve which still had the piercing pin in place....



The velocity you get will depend on the barrel length and the hammer spring chosen.... but you can get an idea from there....

Bob

[grumpy]

Bob, thanks for the great info ! It should help a bunch.

[rsterne]

Going from 800 psi to 1000 psi with a 2240 spring on a 14" barrel will only give you about 20 fps.... If you change to a 1377/2289 spring as well then you should get about 50 fps.... Those are my best guess....

Bob

[grumpy]

This is the guns build.

http://www.gatewaytoairguns.org/GTA/index.php/topic,25244.msg232170.html#msg232170

I am using a modified boss valve. Can I expect to an increase then ?

Dave

[rsterne]

Tough to say.... but I'm betting 50 fps going from 800 psi to 1000 would be in the ballpark....

Bob

[grumpy]

I understand its only a guess. I don't really want to increase the spring tension. It gets too hard for my weak hands to cock. The valve is triple pinned with stainless steel screws for safety sake. Not sure how high I care to push the pressure but I'm thinking no more then 12-1300 psi, though I'm sure It could easily be taken up to 1500. Better to error on the side of caution.

I am building another one very close to the same as the one above, but minus the multi shot breech. It will have the same boss valve but with either an 18 or 24" barrel and disco spring. This one I hope to use for longer range plinking and would like to hit the 750-800 fps with 159 jsb.  Do you think its doable ?

Dave

Tough to say.... but I'm betting 50 fps going from 800 psi to 1000 would be in the ballpark....

Bob

[rsterne]

You will likely need more pressure to hit those numbers.... More pressure requires a heavier hammer spring, there is no way around it.... However, the stock 2240 spring is very weak, going up to a 1377 spring will give you the ability to go as high as 1400 psi and you will hardly notice the increase in cocking force.... it's quite a bit less than a Disco spring, which will give you 1600-1700 psi for a peak....  Even with a 24" barrel, the 2240 spring peaks at about 1200 psi, which means a maximum fill pressure of about 1400....

Bob

[grumpy]

Really appreciate the tips. I have a disco spring I got from you that I am going to have to try. Will report back once its assembled.

Dave

[rsterne]

The heavy spring for the Disco?.... Way overkill but the velocity won't be any higher on a regulated gun.... However, it will likely waste air.... It's a balancing act.... If you have an RVA try backing down the spring preload until you begin to lose velocity.... That way you won't be just blowing extra air out the barrel....

Read the last post I made in this thread....

http://www.gatewaytoairguns.org/GTA/index.php/topic,25524.0.html

It shows what happens to velocity and efficiency with too much hammer spring on a regulated gun....

Bob

[grumpy]

I mentioned the disco spring cause its the only other I have round here. I don't have an  rva on it but have a spare I could.

[rsterne]

Tuning PCPs without an RVA is like working with one hand tied behind your back.... The PRIMARY tuning method is varying the hammer spring and the preload on it.... to balance it against either the fill pressure on a non-regulated PCP.... or the regulator setpoint on a regulated one.... OH! and you need a Chrony....

Bob

[rkr]

Bob, are all Crosman hammer springs the same diameter and length? I have a HPA Nightstalker that I might start tuning next and I'm wondering what springs will fit? Is that Disco spring the heaviest one?

[rsterne]

The springs for the 22XX (CO2 guns), the ones for the 13XX (pumpers) and the Disco are all just under 5/16" OD and about 1.9-2.0" long.... and they are in that order from weakest to stiffest.... The wire sizes are 0.030", 0.032", and 0.035", and the heavy one I sell for the Disco is 0.040" x 1.75" long.... The spring from the 2200 is in between the 13XX and Disco in stiffness, but it's about 2.25" long and I'm not sure of the wire size, all I know is that the Disco spring is stiffer.... I am not familiar with springs in other Crosman guns....

Bob