by B.B. Pelletier

Part 1
Part 2

The test rules
In this test, I wanted to know only if there was anything to the claim that high velocity is an accuracy killer for an airgun. So, here’s how I proceeded. I would shoot ten 10-shot groups at a target 50 yards away. Five would be shot at an average speed of 900 f.p.s. or less and a very tight extreme velocity spread over a 10-shot string. That speed falls right into the range currently espoused by champion field target shooters (850-900 f.p.s.). Five more 10-shot groups were to be fired at an average speed well over 1,050 f.p.s., with an equally tight extreme spread. While the faster shots may not always break the sound barrier, which is variable, they’ll be well within the transonic region, where they should be disturbed in flight by their own shockwave.

The first pellet selected was a Chinese dome. Here’s how it performed.

Whiscombe JW 75 in .177
59 deg. F – Muzzle 1′ from start screen – 10 shots
All pellets lubed with Whiscombe honey

Transfer port restrictor installed
Chinese domes, 9.1-grains
High: 872 f.p.s.
Lo: 866 f.p.s.
Average: 869 f.p.s.
Extreme spread: 6 f.p.s.
Standard deviation: 2 f.p.s.
Muzzle energy: 15.26 ft.-lbs.

Transfer port restrictor removed
Chinese domes, 9.1-grains
High: 1,077 f.p.s.
Low: 1,066 f.p.s.
Average: 1,070 f.p.s.
Extreme spread: 11 f.p.s.
Standard deviation: 3 f.p.s.
Muzzle energy: 23.14 ft.-lbs.

To assure the port restrictor screw was operating consistently, I reinstalled it after shooting the high velocity string and got another low-velocity average of 871 f.p.s., with a maximum spread of 9 f.p.s. Folks, that’s not only good consistency for a spring gun–most regulated PCP rifles can’t do any better. Especially in light of the fact that I was NOT using sorted pellets! Every shot came straight from the factory tin. And after a roll across the lube pad, the pellet was inserted directly into the barrel.

One thing about using lubed pellets in a powerful spring gun–they can diesel. To keep dieseling to an absolute minimum, keep that lubricant as light as possible. The numbers you see in the tables above were achieved with lubed pellets, but I also shot other strings that went faster and had much larger total spreads. I knew those shots were dieseling. By taking pains to lube as lightly as possible, I was able to get very small velocity spreads and repeat velocity at will with the air restrictor in or out. I also learned how to apply the lube just right.

Shooting the gun
I shot the rifle off a very stable bench with a double sandbag rest (forearm and buttstock both rested). I waited out the wind until the shot had the best chance of being on target. And I made sure I was into good shooting form before starting the strings.

One more thing–and this might be important to everybody. While reading about schuetzen shooting of the 19th century, I happened across the fact that the best shooters always oriented each bullet in the bore exactly the same way. They took note of where the mold line was and always aligned it the same in the breech or false muzzle of their gun.

A few years ago, I bought some super-accurate lead bullets from a schuetzen supply house, and they all had a small mark in the nose to help with this orientation. I had completely forgotten about that little fact; but sure enough, when I checked the pellets, I could see a seam on them as well. So for this first test, I used my bifocals to see and align every pellet in the same orientation at loading. The flip-up barrel of the Whiscombe made this possible; I’m not certain how effective it would be in a turnbolt gun like a Marauder or Crosman 2260.

I selected the Chinese domed pellet because it went fast enough at high velocity. Crosman Premier 10.5-grain pellets topped out at about 1,000 f.p.s., which was too close to the low edge for my liking. The Chinese domes were well into the transonic region, and I wanted to get as far into that realm as possible so that any outcome can be supported by a clear velocity distinction–both well above and below the expected accuracy “barrier.”

So, let’s get shooting and let the chips fall where they may!

The best laid plans…
Boy, did those chips ever fall! They fell everywhere–except where they were supposed to! In short, I got skunked.

It was nothing less than I deserved for being so cocky about this test. My first “group” had opened to three inches before the seventh shot was fired! The gun was all over the paper. True, there was a steady 5 mph breeze from the left, but that was no reason for a group that big. My own overconfidence and lack of pretesting had led me right into the trap.

Having humiliated myself so completely, I decided to try a group at high velocity, as well. They were even worse than the slow ones. Inside four shots, I was looking at more than four inches of dispersion! Also, I believe they were actually breaking the sound barrier, because there was a pronounced crack with every shot. It could have been produced by a strong dieseling as well, but since the temperature was 42 deg. F that day, I think they may have gone supersonic. Needless to say, with these poor results, I did not proceed with the test.

On the way home, I wondered what sense could be made of this mess. I didn’t want to abandon the test, but reporting three-inch groups at 50 yards didn’t seem too desirable, either. Then I remembered another test I performed several months back where I learned that the Chinese domes are much more sensitive to wind than either Crosman Premier lites or heavies. Had I chosen the wrong pellets for the test?

Back to the range
The next day, I went back to the range. This time, I was armed with Crosman Premier 7.9-grain pellets as well as Chinese domes. Though initially overlooking them because I thought they were too light, I was now glad to have them available.

All this shooting took place at the end of March 2001–right at the start of spring in the Northern Hemisphere. Many blustery days had passed before I was able to get to the range to fire the first shot. Then my car compounded the problem by suddenly requiring a new transmission! I had been so confident in the planning of this test, but the actual execution quickly brought me back to reality.

The 7.9-grain Premiers came as a stroke of extreme good fortune, for they shoot even faster than the heavier Chinese domes, plus they have much stronger skirts to take the savage blast from the Whiscombe on high power.

Whiscombe JW 75 in .177
60 deg. F – Muzzle 1′ from start screen – 10 shots
All pellets lubed with Whiscombe honey

Transfer port restrictor installed
Crosman Premier, 7.9-grains
High: 906 f.p.s.
Low: 899 f.p.s.
Average: 902 f.p.s.
Extreme spread: 7 f.p.s.
Standard deviation: 2 f.p.s.
Muzzle energy: 14.28 ft.-lbs.

Transfer port restrictor removed
Crosman Premier, 7.9-grains
High: 1,147 f.p.s.
Low: 1,135 f.p.s.
Average: 1,140 f.p.s.
Extreme spread: 12 f.p.s.
Standard deviation: 3 f.p.s.
Muzzle energy: 22.80 ft.-lbs.

The standard port restrictor Whiscombe sends with their guns delivered velocities in the 820s with light Crosman Premiers, so the hole did not need much enlarging. Luckily, I hit it right on the head the first time, with an average of 902. And look at that extreme spread again. Another very tight string.

With the port removed, the pellets were definitely supersonic, as the crack of each shot proclaimed on my basement range. Although the extreme spread opened up a bit, it is still very tight–too tight for all the shots to be diesels. I felt I could return to the range and try again.

The second time around

The best low-velocity group measured 1.718″ c-t-c at 50 yards with Crosman 7.9-grain pellets. All pellets were lightly lubricated. At this velocity (902 f.p.s. average), the pellet is at the upper limit for accuracy, according to the theory that says 900 f.p.s. is as fast as a pellet should go. This group measures just 76 percent as large as the high-velocity group below.

The best high-velocity group measured 2.254″ c-t-c at 50 yards. Pellet was a Crosman Premier 7.9-grain fired through the same barrel as the low-velocity group above. At supersonic speeds (1,140 f.p.s.), the pellet breaks the sound barrier with a loud crack but has probably slowed down to subsonic by the time it reaches the target 50 yards away.

The second day at the range had better weather than the first, but only because I arrived before 8 a.m., when the wind was at its calmest. There was a prevailing breeze of 1-5 mph from my left throughout the session. The temperature was a chilly 26 deg. F–but it was the best day I’d gotten so far, and the absolute last chance to get this test started.

Instead of sorting the pellets by weight, I used them straight from the box. That’s not the way I wanted to do it, but time was forcing such concessions. Since this was not a complete test, I’ll do it over, but I wanted to give some kind of preliminary results of my experience.

I took each pellet and rolled it on a lubed pad before loading. This time I paid no attention to the orientation of the pellet as it was loaded–another detail for the next go-round.

Premier lites loaded with more resistance than the Chinese domes. I attribute part of that to skirt size and part to Crosman’s harder lead alloy.

As before, I shot the slower pellets (902 f.p.s.) first, then switched to the higher speed (1,140 f.p.s.) pellets. Because the wind was picking up and I was freezing, I limited the number of groups to two for each velocity.

The first five shots at low velocity went into 1.4″, but the last five opened that up to 1.741″. The second group measured a slightly smaller 1.718″. That’s for 10 shots off a double-bag rest at 50 yards. The gun was leveled for each shot and, being a Whiscombe, it is completely recoilless.

I then removed the transfer port restrictor and shot the two high-speed groups. Each shot cracked like a .22 long rifle, breaking the sound barrier. The first group measured 2.503″, the second 2.254″.

The combined size of both low-speed groups measure almost 73% the combined size of both high-speed groups.

What does it mean?
Four groups prove nothing. And even when I rerun the test and have 10 more groups to add, they still won’t be conclusive. But the expected correlation between velocity and group size does seem to have been upheld in what I’ve accomplished so far. The largest low-velocity group (1.741″) is still smaller than the smallest high-velocity group (2.254″)–more than a half-inch smaller, in fact.

You might think I let my expectations bias the outcome, but I tried hard not to. By using a double-bag rest (that’s a bag under the forearm and another bag under the buttstock), I’ve removed as much random gun movement as possible. The Whiscombe’s recoilless nature allows it to be rested, where most springs gun shouldn’t be. A higher-power scope might make for smaller groups, but that would seem to work for both velocities. Besides, it would be impossible to mount on this model Whiscombe.

Different pellets might give different ratios of group sizes in this test, but if the theory proves true, any diabolo travelling at subsonic velocities should be more accurate than the same pellet going supersonic.

This test should also be tried with a PCP rifle. At present, there are only a few that have the broad range of adjustability needed, but the Marauder, the Condor and the Air Force Talon should all be up to it.

One final note illustrates the value of 10-shot groups. When I shot the first low-velocity group, the first two shots went into the same hole. Shot three landed more than an inch away, and shot four went into the hole formed by shots one and two. If I were shooting groups containing fewer shots, I might have been tempted to take that three-shot cloverleaf (which measured 0.241″) as a group–calling the other shot a “flier.” With 10 shots, there’s no such opportunity.