by Tom Gaylord
Writing as B.B. Pelletier
This report covers:
- Adjust the pressure
- R9 disassembly and assembly
- JSB Exact
- Predator Polymag
- H&N Field Target Trophy
- H&N Baracuda
- Crosman Premier
- Benjamin Cylindrical
- Cocking effort
Today we look at adjusting the Vortek Center Latching Air Piston, which I refer to as the center-latching unit (CLU). It went faster and easier than I imagined.
Adjust the pressure
To adjust the air pressure in the unit I had to disassemble the Beeman R9, to get the unit out. That procedure is described in Part 1. Once the unit is out, the piston seal has to be removed to reveal the air port.
To adjust the pressure in the CLU, first release all the air. That way you start from zero. The unit fills very fast from a hand pump and this is the best way to ensure accuracy.
The air is released by pressing against the ball valve with something small — I used an Allen wrench about 1/16-inch in diameter. Tap it with a hammer a couple times and then you can just push to release the rest of the air. There isn’t much!
When the air is out, attach the fill adaptor and connect it to a high pressure hand pump. The o-rings on the adaptor Vortek sent me are not to seal air. They are there in place of knurling. That adaptor was made up fast and they didn’t want to change the tooling in their machine to cut knurling. The o-rings are just for grip.
I filled the CLU and made a mistake when I did. I want to cover that right now. We will get back to the main report in a moment.
I filled the CLU to what I thought was 500 psi. Last time we looked at the performance on 675 psi, which Vortek says should generate about the same velocity as the factory mainspring.
R9 disassembly and assembly
Tom Gore advised me to put a smear of moly grease behind the piston seal, where it would burnish into the compression chamber. I did that with a cotton swab before putting the CLU back into the spring tube.
I complained in the previous report about how long this new R9 took me the first time I disassembled it. This time it came apart and went back together in 45 minutes. The parts were just looser from disassembly, plus I was becoming familiar with the R9.
When I tested it after this work, though, it cocked harder than it had the first time — which was 36 lbs. And the velocity was higher. What?
Man, was I discouraged! I went to the hand pump to make sure I had done things right, and of course I hadn’t. The gauge on the pump reads in both bar and psi, and I had read the bar scale when filling this time. Instead of 500 psi I put in 50 bar, which is 725 psi.
I could have just tested the rifle from there, but I wanted to test it on lower pressure first, so I went through the entire thing again — disassembly, pressurizing the CLU and assembly. This time the entire procedure took me 30 minutes — start to finish.
I’m not trying to set a record for speed. I’m just saying it gets easier as you become more familiar with the procedure. This time I watched the gauge closely and made sure that just 500 psi were put into the CLU. And, what a difference it made!
I will say this — the CLU takes a few shots with the rifle to settle after you change the pressure. My first couple shots with 500 psi were almost as fast as they had been before, plus the gun seemed only slightly easier to cock. After several shots, though, things settled down to what they are going to be. Let’s look at that now.
First to be tested were JSB Exact domes. When the CLU was at 675 psi they averaged 689 f.p.s with a 21 f.p.s. spread. After pressurizing to 500 psi the average was 544 f.p.s. and the spread was 16 f.p.s. — from 539 to 555 f.p.s. At the average velocity this pellet generated 9.02 foot-pounds at the muzzle.
Next to be tested were the Predator Polymag hollowpoints. In the last test (675 psi) they averaged 672 f.p.s. with a 16 f.p.s. spread. On 500 psi they averaged 531 f.p.s. with a 10 f.p.s. spread from 526 to 536 f.p.s. That’s 8.14 foot-pounds at the muzzle.
H&N Field Target Trophy
We learned that the H&N Field Target Trophy is Vortek’s favorite pellet in .20 caliber. In the last test these averaged 763 f.p.s. with a 9 f.p.s. spread This time they averaged 610 f.p.s. The spread went from 606 to 619 f.p.s, which is 13 f.p.s. At the average velocity these generated 9.44 foot-pounds.
Now it was time to try the H&N Baracuda pellet. At 13.58 grains they are not heavy pellets in .20 caliber. They averaged 676 f.p.s. before with a 9 f.p.s. spread. This time they average 548 f.p.s. with a 9 f.p.s. spread from 543 to 552 f.p.s. They produce 9.06 foot pounds at the muzzle.
I tested .20 caliber Crosman Premiers. Although they are no longer available I have several boxes of the 14.3-grain domes, so I thought I would test them. In the last test Premiers averaged 662 f.p.s. with a 15 f.p.s. spread. This time they averaged 528 f.p.s. and the spread was 13 f.p.s. — from 521 to 534 f.p.s. At the average velocity Premiers produced 8.85 foot pounds of energy.
The last pellet I tested was the Benjamin Cylindrical. In the first test these averaged 642 f.p.s. with a large spread of 46 f.p.s. This time they averaged 544 f.p.s. with a 19 f.p.s. spread from 534 to 553 f.p.s. They produced 9.40 foot pounds of energy.
Dropping the pressure of the CLU from 670 psi to 500 psi dropped the muzzle energy from 13-15 foot-pounds to around 9 foot-pounds. In most cases the velocity spread got tighter at the lower pressure.
The rifle became even smoother shooting because the piston isn’t moving with the same force. In fact at this pressure this R9 is feeling more like an R8. I would enjoy this gun in .177 because it is so easy to shoot.
While I had the rifle apart the first time I removed all the Weihrauch grease from the Rekord trigger and lubed the critical points with moly grease. I also lightened the trigger return spring. The trigger that had some second-stage creep and broke at 2 lbs. 2 oz. before now breaks crisply at 1 pound.
This is what I was after when I decreased the pressure in the CLU. I wanted smoother shooting and lighter cocking. When the CLU had 670 psi, the rifle cocked with 36 lbs. of effort. With 500 psi it now cocks with 27 lbs.
This test shows a flexibility that I haven’t seen in a spring piston air rifle other than the Whiscombe with its air transfer port limiters. I wish I could keep the rifle with this tune, but there is one more thing to find out. What is the maximum power that can be derived?
I will not be over-pressurizing the CLU the way Theoben owners used to do. I think where I had it at 50 bar, which is 725 psi, is a good practical maximum. So, that’s where we will go next.