.25 strange readings

[villaman]

My .25 mk2 with power plenum fit last week , starts off at 970 FPS for about 5 shots then after drops to 958 for about 5 shots then keeps going down to 930 
Reg setting 125 bar . I changed reg O ring last week

any idea what it might be ?

 

[nervoustrig]

That sounds like the input regulation characteristics of the regulator. It’s probably producing a higher pressure when the reservoir is full than when the reservoir is lower. Can you see any evidence of this on the gauge showing the regulated pressure?

If so, try backing off the hammer spring tension slightly. To set it, crank up the hammer spring tension until the velocity no longer increases, then back it off to somewhere between 95 - 97% of that maximum.

 

[villaman]

That sounds like the input regulation characteristics of the regulator. It’s probably producing a higher pressure when the reservoir is full than when the reservoir is lower. Can you see any evidence of this on the gauge showing the regulated pressure?

If so, try backing off the hammer spring tension slightly. To set it, crank up the hammer spring tension until the velocity no longer increases, then back it off to somewhere between 95 - 97% of that maximum.

Do you think it might be a faulty reg . I know my reg gauge is not reading right 

 

[nervoustrig]

That’s hard to say without knowing the extent to which it’s varying. Some amount of nonlinearity can be expected and usually it can be rendered inconsequential by tuning to the velocity knee as described above. The only way to know is to try.

 

[Jlacouturec]

maybe regulator needs maintenance... take it out and lube/change orings!

 

[nervoustrig]

Well, either the O-rings seal or they don't. They do not influence the setpoint repeatability in any meaningful way. The forces from the Belleville washers and the counteracting force from the output side are vastly higher than anything contributed by the seals.