Understanding the performance/power curve of a PCP

by B.B. Pelletier

This final blog of 2008 was inspired by several questions from reader Kevin but also from other readers who are now owners of precharged pneumatic (PCP) airguns. I’ve written these things before, but perhaps never put them in the same order as I will today.

A PCP valve operates best between a certain high and low pressure point. That is to say the valve will open and remain open long enough to pass air from the reservoir to power a pellet to more or less the same velocity. When the reservoir pressure is high, it acts on the valve to close it faster, but the air that passes through the valve when the gun fires is under a lot of pressure. As you continue to shoot and the reservoir pressure drops, it acts with less force and less quickly on the valve to close it, so the valve remains open slightly longer. The air that passes through the valve before it closes is not pressurized as high; but since the valve remains open slightly longer, it delivers similar acceleration to the pellet. The result is that the pellet stays at the same velocity, more or less, throughout a number of shots.

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Career Infinity by Shin Sung – Part 3

by B.B. Pelletier

Part 1
Part 2

Let’s look at the Career Infinity velocity. The new inlet seal I showed you yesterday is working fine, and it may turn out to be the fix for this problem. I’ll let you know at the end of the accuracy report, when the gun has been filled many more times.

You may recall that this gun doesn’t shoot the pellets from the cylinders. It pushes them into the breech with a bolt probe, and that’s where they are fired from. That way the long gap from cylinder to breech is a non-issue, as far as accuracy goes. The pellet begins its flight while already in contact with the rifling.

However, there are two observations I will make about the cylinders. First, they do not rotate far enough to align with the bore during the cocking stroke. After cocking, I had to advance the cylinder another half turn to get the pellet chamber aligned with the bore. You know that because the bolt probe won’t align with the chamber in the cylinder, which prevents the sidelever from closing. That held true for both cylinders that came with the gun, and it takes away some of the speed you get from the rifle being a repeater.

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Odds and ends Removing the Diana 27 seal & fixing the Infinity inlet seal

by B.B. Pelletier

It’s too cold to shoot CO2 outdoors, so the accuracy test of the Crosman 1088 is postponed until we get some warmer days. So, I thought I’d clean up a couple of jobs that I’m working on and show them to you as I go. First, I removed the leather breech seal from the Diana 27 rifle.

Derrick found an inexpensive set of leather punches for me at Harbor Freight, so I ordered them to use in the Diana 27 breech seal project instead of just carving the seal from a leather belt with a sharp knife. There are nine graduated punches in the set for less than $5, so even with shipping I figured it was well worth the investment. I’ll probably have to trim the seal to final size, but the punches will get me most of the way there.

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Diana 27 – Part 2

by B.B. Pelletier

Part 1

Today we’ll look at my .177 Diana model 27 rifle after the piston seal and breech seal have been soaked in oil. I told you I put petroleum oil down the air transfer port because my gun is a low-powered springer with leather seals. Leather seals need lots of oil to keep them fresh and pliable, and a low-powered springer doesn’t generate enough compression to detonate the oil. So, petroleum-based oil is fine for guns on this category.

The way to know for certain that you’ve oiled the piston seal enough is to move the barrel through the first few inches of cocking and then relax it. Do that several times and listen carefully to the air transfer port. When you can hear a slurping sound coming from the port, the piston seal is soaked with enough oil to rejuvenate it.

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Merry Christmas 2008

by B.B. Pelletier

Merry Christmas!

I was interviewed on the Arizona radio program, America Armed and Free last week. You can listen to that interview here, if you like. It will be available for one more week.

Today I’ll share a couple of my favorite gifts with you, and maybe you readers can let us know what you got. For those who don’t celebrate Christmas, you can either tell us about your most recent acquisition or just sit back and enjoy the party!

The man who has everything
What does Tom Gaylord’s wife give him for Christmas–the man with the entire airgun world at his fingertips? While that’s not entirely true, a lot of people think it is. They think I can have anything I want.

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Buying a high-pressure air tank – Part 2 1000 posts!

by B.B. Pelletier

Part 1

Today’s post is the thousandth since we began in March 2005. How fitting that it should come on Christmas Eve. Regardless of your religious views, we all owe Pyramyd Air thanks for their gift of this blog that has lasted so long. Let’s hope we’ll still be enjoying it after another thousand reports!

Although Abe asked for this report, I’ve heard from a lot of other readers who had questions and comments about air tanks. I’ll try to address them all today.

Lloyd wants me to tell you that you should buy the largest scuba tank you can afford. He also says to tell the dive shop operator to please fill the tank to the max, because divers are less concerned with pressure than we are. His most important message, though, is to get to know the people at your dive shop. I couldn’t agree more. I’ve seen airgunners ruin their entire PCP arrangement by simply alienating the dive shop personnel. And I’ve gotten many concessions and good treatment because I acted as though the dive shop was doing me a favor–WHICH IT IS. A little civility goes a long way when dealing with an owner/operator, like the guy who runs the dive shop.

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Diana 27 – Part 1

by B.B. Pelletier


Diana model 27 is a classic breakbarrel. My new one is a .177.

Kevin prompted this report by asking me about the Diana 27 I bought at this year’s Roanoke airgun show. Then he surprised me with the gift of a very nice peep sight made for the Diana model 75. It also works great on the little Diana 27 rifles, and Kevin wanted me to see that so he sent one.

What I plan to do is test my new .177-caliber model 27 and then install the peep sight and test that for you. Unfortunately, the 27 I got in Roanoke doesn’t have a rear sight base for this sight; I’ll install it on my other 27, which is a Hy-Score 807 in .22 caliber. For those who are fascinated by coincidences, the .22 caliber Hy-Score was purchased from the same dealer from whom I bought the .177 15 years before. It was made in August of 1967, while the new gun was made in March of that same year. Spooky, no?

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