I've been tuning my P35 and P35X and got a little lost so I started removing the regulator to change it and doing some measurements. There are no markings on the regulator to tell you what setting of the adjustment screw gives you what regulator pressure. I am also unaware of a regulator tester for spa regulators. If you know of one I would love to spend a little money and get one. Anyway, so we have a regulator and we want to make a change, how do we know where to turn the screw to? I think the paper tape that Huma puts on theirs is a bit of a clue. I have a Huma in my Caiman and I had to remove excess silicone grease from its washer stack and put a little on the O-ring of the adjustment screw after I got the gun. So I've had it apart. I did not take measurements of the two but just looking at them the SPA regulator looks a lot like the Huma. But the point I am getting slowly towards making is the Huma markings are for one turn or less of the regulator stem. I think the useful settings of the SPA are probably similar. All occur in about one turn of the adjustment stem. But where do we start?
I have not done the work to tell you exactly what length correlates to what regulator setting but my guess is whatever I told you would not be exact for your regulator anyway. I'm messing with two guns that are not acting right and I suspect there is a fair bit of tolerance in the SPA parts. But I think we should target about 50 mm length. The picture shows how I measure it with a digital caliper. The stem moves about 0.5mm for one turn. I don't think you can go up in length (and regulator pressure) a lot but I've used 50.15 successfully before. So maybe 49.? (6?, 7?, 8?) to 50.2 would be useful lengths to try. Again, a shorter length will be a lower regulator pressure. A longer length will be a higher pressure.
What I recommend is to set the length to about 50mm. Say between 49.95 and 50.05. The point is not that you have to be ultra precise, you are just trying to get in the ballpark. I have the regulator in my P35X set this way and it is giving me about 700 fps on 25.4s, for example. It seems to be working but blew out an O-ring yesterday so I need to shoot it a bit more to be sure. This P35X has a 450mm barrel so it's velocity will be low, I am trying to set it up around 30 fpe for a pretty good shot count and plenty of power for squirrels. So I have one data point to say a regulator length of about 50mm will work but result in a lower power than a lot of you probably want. Turning it up 1/4 turn would be .125mm and about the maximum I would try next if I wanted more velocity/fpe. If I wanted less I would shorten the regulator by a similar amount.
I don't know what SPA guns use the same regulator but my 3 P35s, my one bullshark, and my one P35X all seem to. I've interchanged them between guns. I'm guessing the Scout and Ranger may be the same and I wonder if the two new Dianas might also have the same regulator.
I have not done the work to tell you exactly what length correlates to what regulator setting but my guess is whatever I told you would not be exact for your regulator anyway. I'm messing with two guns that are not acting right and I suspect there is a fair bit of tolerance in the SPA parts. But I think we should target about 50 mm length. The picture shows how I measure it with a digital caliper. The stem moves about 0.5mm for one turn. I don't think you can go up in length (and regulator pressure) a lot but I've used 50.15 successfully before. So maybe 49.? (6?, 7?, 8?) to 50.2 would be useful lengths to try. Again, a shorter length will be a lower regulator pressure. A longer length will be a higher pressure.
What I recommend is to set the length to about 50mm. Say between 49.95 and 50.05. The point is not that you have to be ultra precise, you are just trying to get in the ballpark. I have the regulator in my P35X set this way and it is giving me about 700 fps on 25.4s, for example. It seems to be working but blew out an O-ring yesterday so I need to shoot it a bit more to be sure. This P35X has a 450mm barrel so it's velocity will be low, I am trying to set it up around 30 fpe for a pretty good shot count and plenty of power for squirrels. So I have one data point to say a regulator length of about 50mm will work but result in a lower power than a lot of you probably want. Turning it up 1/4 turn would be .125mm and about the maximum I would try next if I wanted more velocity/fpe. If I wanted less I would shorten the regulator by a similar amount.
I don't know what SPA guns use the same regulator but my 3 P35s, my one bullshark, and my one P35X all seem to. I've interchanged them between guns. I'm guessing the Scout and Ranger may be the same and I wonder if the two new Dianas might also have the same regulator.