by B.B. Pelletier

Part 1

Today I’ll shoot the Benjamin HB22 air pistol for velocity, plus I’ll also do some interesting pneumatic experiments to demonstrate how these guns work. As I test this gun, you’ll see that a multi-pump is really a self-contained airgun experimental lab. Because of the length of these tests, I will do an accuracy report in another part of this report.

First test: How many pumps?
This test demonstrates how velocity varies as you add pump strokes to the gun. There are some interesting side effects here, as well. I will also cock and fire the gun after each shot to determine whether any air remains in the reservoir. I used a 14.3-grain .22 caliber Crosman Premier pellet, which is identical in weight and shape to a .22 caliber Benjamin Sheridan Diabolo.

Pumps—–Velocity—–Air remaining?
2*————236—————No
3————-288—————No
4————-326—————No
5————-355—————No
6————-377—————No
7————-390—————Yes
8**———-405—————Yes
9————-414—————Yes
10————425—————Yes
11————429—————Yes, lots
12————432—————Yes. Enough for a 2nd shot
2nd shot—-256—————No
* Below the recommended minimum number of pump strokes
**Maximum recommended pumps

Benjamin recommends a minimum of three pumps and a maximum of eight for this pistol. You will notice that starting at the seventh pump, there was air remaining in the gun after the shot. I went beyond the recommended maximum number of pump strokes to see what would happen. In an air rifle, the power usually begins to decline right away. With this pistol, it kept increasing, although the amount of the increase diminished with each additional stroke.

By the 11th stroke, the air remaining in the gun after the shot was significant, so following a try with 12 pump strokes, I cocked the pistol again, loaded another pellet and fired a second time without pumping. Notice that the second shot has greater velocity than the gun had with two pump strokes.

Before you decide that additional pump strokes are the way to go, let me tell you that the strain on the pump mechanism was enormous. After the 10th pump, I could barely pop the pump handle away from the tube, and the pressure to close the pump handle probably reached 50 pounds. If you did this regularly, you’d wear out the pump mechanism to the point that a major rebuild would be required. In fact, if you look at the data, it suggests that this particular pistol is better off with a maximum of just seven pumps strokes instead of eight.

How consistent?
This test demonstrates how consistent the velocity is for the same pellet and same number of pump strokes. Once again, I used a 14.3-grain Crosman Premier domed pellet. Every shot was the result of five pump strokes.

Shot——Velocity
1————-340
2————-338
3————-340
4————-340
5————-341
6————-340
7————-341
8————-339
9————-340
10————341

You don’t get consistency this good from a regulated Olympic 10-meter target rifle costing $3,000. I expected this, because I’ve seldom seen more than six f.p.s. shot-to-shot variation in multi-pump rifles when I did this test, but this is the first multi-pump pistol I’ve tested this way.

Fast vs slow pump strokes
Does pumping the gun fast make any difference? In this test, I will pump the first five shots with a slow and deliberate pump stroke, allowing two seconds for air to rush into the compression chamber when the pump handle is fully extended. That will be followed by five shots using a rapid pump stroke. I will pump as fast as I can for this one. In both tests, the gun will be pumped a total of five strokes per shot, and I’m still using Premier pellets.

Slow pumping
Shot——Velocity
1————-340
2————-339
3————-338
4————-339
5————-339

Fast pumping
Shot——Velocity
1————-339
2————-341
3————-340
4————-340
5————-340

Not much difference, is there? In fact, all 10 shots fit neatly into the other 10 of the consistency test.

You will also notice that the pistol got 355 f.p.s. on five pumps in the first test, yet in both the test for consistency and the test for how fast the gun was pumped, the shots never got above 341 f.p.s. What’s happening there? Well, I did test for remaining air and found none, so that’s not the explanation. I do know the count of the pump strokes was correct, so maybe the best way to check this test is to do it again the same way. Premier pellets once again.

How many pumps? (second test)
Pumps—–Velocity—–Air remaining?
2*————224—————No
3————-275—————No
4————-311—————No
5————-340—————No
6————-358—————No
7————-376—————Yes
8**———-388—————Yes
9————-399—————Yes
10————407—————Yes
11————418—————Yes, lots
12————424—————Yes. Enough for a 2nd shot
2nd shot—-275—————No
* Below the recommended minimum number of pump strokes
**Maximum recommended pumps

This second test was conducted after the consistency test and the pump speed test. Note that the air remaining in the gun after shot 12 is now equal to three pumps! After this test, I chronographed the gun five times on five pumps of air and got five identical velocities of 335 f.p.s. So it seems the over-pumping is having an immediate effect on velocity – lowering it rapidly. I do not intend conducting more testing of an over-pumped gun.

This is the first hard proof I’ve ever seen that over-pumping harms a multp-pump pneumatic. Perhaps it happened so fast because this is a pistol, and the springs have to be smaller to fit inside the smaller valve mechanism. Whatever the reason, the top velocity has definitely been reduced.

I want to impress upon you the fact that each air pistol will be unique. How you treat them will also determine how they perform. If one owner follows the instructions and another routinely over-pumps his pistol, the first pistol will be faster than the second one right away, pump for pump.

Tomorrow, I’ll do the accuracy test, plus I’ll do another interesting velocity test.