BB’s Christmas gift: Part 2
by Tom Gaylord
Writing as B.B. Pelletier
Like all Supergrades, my new rifle is graceful and attractive.
This report covers:
- The test
- Pump head may need adjustment
- Compare to the other Supergrade
- The other Supergrade
- Test 2 — stability
- Four pumps
- Sick old girl!
- Test is suspended
Today we look at the power of my new Sheridan Model A, also known as the Supergrade. My low-serial-number rifle was probably made in the 1940s. The wood has certainly been refinished. The rifle seems to function fine, though today will be the very first time I have tested it over a chronograph.
I had pumped the rifle twice when I put it away, and it had held the air when I started this test. That’s a good sign.
I decided to perform my standard test on the rifle, starting with an assessment of the velocity/power at each pump stroke, from 3 to 8. For this test I used .20 caliber Crosman Premiers that are no longer available. It was very revealing.
The first shot on 5 pumps was recorded at 383 f.p.s., so I decided to shoot a second time. When that one registered 353 f.p.s., I knew the first shot was recorded correctly. What’s going on?
Pump head may need adjustment
One clue is the pump arm. After 4 pumps (pumps 5 to 8) the pump arm springs up when I open it to pump. That’s a sight of some compressed air remaining in front of the pump piston head because it’s not entering the reservoir. It means the space between the end of the pump piston head and the air reservoir inlet valve is too large when the pump handle is closed.
These older multi-pumps were made with threaded pump rods, so this space can be adjusted as close as possible. Part of any tuneup is to adjust this distance to as close as you can without the head touching the inlet valve.
Too close and the pump head gets damaged, which can be another reason why this happened. If the pump head is adjusted too close to the inlet valve, it may have been pressing against the valve and the pump head may now have a crater in its end. The only way to fix that is to either get a new head or to fill the crater and adjust the head so it doesn’t crash against the inlet valve.
I don’t know what the problem is at this point, but this test shows there definitely is a problem. I want you veteran multi-pump owners to know that at 5 pump strokes and above I cocked the rifle and fired it a second time to hear whether any air remained after the shot. None did, though 8 pumps.
Compare to the other Supergrade
If this was our first excurion into Supergrades we might wonder where this rifle was, but fortunately I tested another Supergrade last October. That rifle also had some valve problems, but look at the results it gave for the same test.
The other Supergrade
This other rifle was not without its faults, but the power it developed was significantly greater on each pump stroke. This is a classic example of why a chronograph is such an important tool for the airgunner.
Test 2 — stability
Looking at the first test, I decided to test the rifle for 5 shots with Premiers on 4 pumps next. That seems to be the best spot for the rifle at this time. This test was an eye-opener!
What a test this was! The low velocity on the first shot told me that more is wrong with my rifle than just the pump rod out of adjustment. But that was just where it started.
On the second shot, the rifle failed to fire! I recocked it and shot again and once more, nothing. So I cocked it again (you have to cock a Supergrade before you pump it or the valve won’t hold air) and then pumped it 4 more times. That gave me 401 f.p.s. After the shot I cocked it again and fired. There was no air left in the reservoir.
The same thing happened on each successive shot. The first time, nothing. Then pump it again and fire and it worked. This is similar to what the other Supergrade did, but not quite the same.
After shot 4 I cocked the gun and fired it and there was air remaining in the reservoir. This was the only time that happened.
Sick old girl!
I think this test reveals that my new Supergrade is a sick old girl. I have seen similar problems with every Supergrade I have shot, and I think it comes down to the valve design. The Supergrade valve is a ball, rather than a tapered plug. I think it works fine when new, but over time the valve seat wears and hardens to the point that things like this start happening.
The Supergrade valve is a ball, rather than a tapered plug. It works well when new, but when it gets old there can be problems. I think it’s due to the valve seats hardening with age.
Valve seats in all pneumatic guns harden with age. but when they are replacxed the guns work like new again. The problem is, new Sheridan valve seats are not available. Even if you were to find a supply of new-old-stock Sheridan Model A valve seats somewhere, they would have hardened with age just sitting on the shelf and would not be any better than the seats in your gun.
Other airguns have similar problems. Diana recoilless airguns, FWB 124s, Hakims and Walther LGVs all had piston seals that went bad with time. I showed that you you dramatically when we looked at the
time-capsule FWB 124 I once owned.. Click on that link and scroll down the page to see what I mean.
Test is suspended
This is as far as I will go today. The rifle isn’t performing well and I need to do something to improve it, if I can. When I do I will bring it back and continue the report for you.