Help with a Caiman velocity spike

[Bravo1956]

So I love my Caiman in 22 but I noticed a different pitch in the sound when it gets to around 180 bar, so I put my FX chrono on and noticed that at around 180 bar the fps increases from 870 to 950 plus!
I had it set to shoot 16 gr JSB at 870, charge it to 300 bar and it was great for 50 shots, until around 180 bar and I could hear it had gotten faster, chrono says 950 plus?
Any thoughts?

 

[hussn32]

Sounds like a regulator problem

 

[nervoustrig]

With a regulated airgun, rising velocity is an indication the hammer spring tension is set too low relative to the regulated pressure. What happens is, as the pressure falls, the hammer has an easier job knocking the valve open because there is less pressure resisting it. The result is more air released -> higher velocity.

Another side effect is that the extreme spread will not be as tight as it could be.

The solution is to fill back up to 300 bar (or something well above the regulator's setpoint). Then incrementally increase the hammer spring tension and fire a shot over the chronograph. Keep repeating until the velocity no longer increases. Then back off the hammer spring tension until the velocity falls to about 97% of the maximum. So let's say it tops out at 980fps, you'd back off the hammer spring tension until the velocity falls to something close to 980 * 0.97 = 950fps.

It may be that this hypothetical 950fps is higher than you want. Maybe accuracy suffers, shot count is lower than you'd like, etc. In that case what you'd do is dial down the regulator to a lower pressure and once again adjust the hammer spring tension to 97% of maximum velocity.

When the gun is adjusted in this manner, the velocity will gently taper off once the pressure falls below the regulator's setpoint. The extreme spread will also be improved.

 

[Tomygun1]

Hey,
I also own and love my Benjamin Craftsman series Cayden 22 and have noticed similar fluxuations. As you know these are not regulated guns so you can rule that out as a problem. Mine behaves like you describe and I have been thinking of adding an aftermarket regulator to it to over come the pressure variance. After playing around with the venturi power adjuster and trimming the hammer spring the velocity still fluctuates. But it remains soo accurate at 75yds @960fps with JSB or Sig pellets that Im tempted to let it be. I will likely ad a regulator just to see what happens.

 

[nervoustrig]

Caiman or Cayden?

Regulated and unregulated, respectively.

 

[Bravo1956]

Yes I am thinking that the reg is way too high, the issue is it is not easy to adjust and I have not found any media on how to access it?
I don't want to tune the hammer up to shoot 16g at 950, I do not like how it sounds or feels at that level.
I may tear into it this winter, but it is consistent and very accurate like this between 300 and 180 bar even thought it is out of balance.

 

[Bravo1956]

So I have concluded that the reg does not like 300 bar, I shot I'd down below reg setting, like to 90 bar then filled to only 250 bar and adjusted HS to shoot 16s at 870 and have not had any issues. I think setting filled at 300 bar was not good for the reg.

 

[douger]

300 bar lotta air presure i sure wouldnt fill my guns that high hard on regs unless you got duel regs

 

[MikeVV]

I stop at 250 bar during the fills of my Caiman (and the X).
I've not heard any difference in the shot sound in either of my guns. I normally stop at about 130 or 150 bar to refill.

I've got both of my Caimans adjusted down to about 800fps, (a touch over).

Mike

 

[Bravo1956]

Yes I agree and have learned that also. I have filled my Uragan 25 to 300 bar for a year and no issues, but after this I am only going to 250, plenty of shots at 250.