by B.B. Pelletier
Mr. B. requested this one–comparing regulated precharged pneumatics to unregulated PCPs.
What is a regulator?
First, what is a regulator and how does it work? A firing valve in a PCP does not operate at its peak at 3,000 psi–not even close. Most of them work best down around 2,000 psi and some work best at even lower pressure. But, the fact is that they still do work acceptably well at higher pressure. So, the gun gives a string of shots at a more or less constant velocity until it drops below the lowest pressure at which the valve functions well.
Just above the top-end operating pressure, the valve starts closing sooner than it should. When a certain pressure is exceeded, the gun begins to shoot slower than it’s capable of shooting. It continues to do this until the internal pressure drops below the point where valve lock starts happening.
An air valve has a range of pressure–from low to high. As long as the air that’s supplied to it stays within that range, the gun shoots at a constant velocity, more or less. And it’s the “more or less” that’s of great concern to airgunners.
An unregulated gun
I have a Daystate Harrier that operates best between 2650 psi and 2,000 psi. In that range, I get 24 shots of 10.6-grain Beeman Kodiaks going about 920 f.p.s. They will not vary more than 20 f.p.s. throughout the entire range. But fill to 2700 psi, and the pellet might go only 880 f.p.s. for the first two or three shots. Continue shooting after the 24 good shots (pressure falling below 2000 psi), and the velocity drops again into the 800s.
That is what a fairly good unregulated gun will do. I’ve seen better ones that would keep their strings within 10 f.p.s. throughout the range. All valves are not of equal quality and stability. I’ve also seen valves that varied more throughout their range. The AirForce Talon SS will often vary by 30 f.p.s. throughout its range, yet still shoots half-inch 5-shot groups at 50 yards.
A regulated gun
What about a regulated gun? Well, a regulator lowers the pressure of the reservoir to an ideal level before making it available to the valve. You might want to read my report on the air pressure regulator. If I installed a regulator in the reservoir of my Harrier, I could probably drop the velocity variation within the string of shots from 20 f.p.s. down to 10 f.p.s. or, perhaps, even less. I’ve tested PCP guns that varied by only two f.p.s. throughout their entire string of usable shots.
However, by installing a pressure regulator with its firing chamber inside the reservoir of my Harrier, I’d be subtracting volume from the reservoir. In other words, less room for air. That could be offset by increasing the pressure in the reservoir, but there’s a point beyond which the regulator will not operate. So you can’t just keep increasing the pressure indefinitely.
What are the benefits?
How would I benefit if I installed a reg in the Harrier? Well, quite probably I would pick up a shot or two. Experience shows that with small reservoirs, like the one in the Harrier, a reg will add only a shot or two to the total string. And all the shots would be closer in velocity because the firing valve would be working at the ideal pressure. The question I have to answer is if I think it’s worth a couple extra shots and a slightly tighter velocity variation to go to the trouble of installing a regulator.
I decided that it wasn’t, because my Harrier operates at a nice low max pressure. It’s easy to pump to 2650 psi; much easier than to pump to 3,000 psi. At least, it is for me.
On the other hand, my Career 707 went from 30 usable shots to over 60 at the same power with a regulator. And the velocity variation of those shots dropped from over 30 f.p.s. to around 10 f.p.s. In that case, it was definitely worth the effort to install the reg.
Some things to consider
Some guns aren’t suited for regulators. The AirForce guns, for example, cannot be easily regulated because of how their tanks are made. Any regulator would have to be external to the tank, which would add to the rifle’s length of pull. The Benjamin Discovery has a small reservoir like the Harrier, so adding a regulator might not gain an advantage in total shots, but it might tighten the extreme spread of the string, which is on the order of 30-35 f.p.s. right now.
The final thing I want to say about regulators is they will all fail at some point. That’s a fact that cannot be denied. I’m not talking about decades of time, either. Regs are not known for lasting a long time. The greater the pressure differential (difference between reservoir pressure and firing pressure) they must deal with, the shorter their life tends to be. When they go, you usually end up with an unregulated gun. In some cases, you have a broken gun that has to be repaired to work at all.
For that reason, Larry Durham decided not to regulate the design of what became the USFT rifle. He felt it’s better to have an easily repairable rifle than to have a super-tight velocity spread. The USFT won the 2007 Field Target World Championship.
Here are my personal feelings. I like regulators on 10-meter guns, where they seem to last a long time. But on a sporting airgun, I like an unregulated but balanced valve that I know will outlast any regulator. However, when the reg is working, it makes for a wonderful airgun experience. I cannot deny that.