Tuning overlap

[Mopo]

Let's say I'm aiming for a target (pun intended) of 850fps. I can get that at one regulator setting with the hammer spring mostly turned out. I should also be able to reach the same velocity with the hammer spring most of the way in and the regulator pressure turned down a notch or two.

The regulator is currently set to about 1,900 psi and the hammer spring tension is a couple of turns in from all the way out. Within that range I see a fairly flat shot string and fairly decent shot count. I'm using a hand pump, pumping up to around 3,000 psi and refilling again when the pressure goes down to about 2,100 psi.
 
I'd like to learn what advantages/disadvantages there are by biasing the settings towards one end or the other. I'm interested in maximizing efficiency, of course, but living in Canada where sound suppression is illegal my primary goal is to bias the tune towards achieving the lowest possible sound output. From empty it takes about 350-400 pump strokes to bring the tank up to pressure so I'd prefer to minimize the amount of experimenting I need to do that involves degassing to change regulator settings. 

[rsterne]

Read through this thread.... https://www.gatewaytoairguns.org/GTA/index.php?topic=74919.

It should answer your questions.... The best way to tune a regulated PCP is on the "knee", whereas the two extremes of tuning you mention would be on the "plateau" or on the "downslope".... Either has problems, as described in that thread.... Tuning on the downslope (higher pressure with minimum hammer strike) will produce the quietest performance and higher efficiency, but you may experience a large variation of shot-to-shot velocity, and below the regulator setpoint the velocity will increase as the pressure drops.... The reasons why are explained in that thread....

Bob

[Mopo]

Thanks Bob. You have a clear, concise, and easy to understand writing style that makes it easier to understand these concepts. I'm guessing you did a fair amount of technical writing in the past.

I did read your thread last year but having read it again just now it makes more sense to me. I'm more or less at the knee now, about 6% down from peak. I don't see any increase in fps as I pass the setpoint, so it seems I have a bit of leeway to tune towards the downslope given that I normally refill a bit before before reaching the setpoint.