Myths of the multi-pump
by B.B. Pelletier
When I started The Airgun Letter back in March 1994, I did so out of frustration. I had just subscribed to American Airgunner magazine and they folded, leaving me with half a subscription unfulfilled and an unquenchable thirst for more information about airguns. I could buy all the gun magazines I wanted, because there were over a dozen titles on the newsstands back then, but there was never one about airguns. And, the few articles gun writers wrote about airguns were trash back then…just as it is today.
Edith suggested that I write my own magazine about airguns, and I thought she was crazy. I told her I didn’t know enough about them to fill a whole magazine, so she suggested that I write a monthly newsletter, instead. I still thought she was out of her cabeza, but at her suggestion I sat down one day and wrote the titles of all the articles I knew I could write about. When I had three-and-a-half legal sheets filled with one-line titles (about 150 titles) I figured it might be worth a try.
The rest of the story is that we started publishing the newsletter in March 1994 and added 50 percent more pages a year later because I needed the extra space. Then, we also published six different 100-page magazines called Airgun Revue, for which I wrote historical airgun articles.
The only reason we stopped publishing the newsletter was we were losing money. People were copying the newsletter and sending it to their friends. I had thousands of readers the world over, but most of them were not paying for a subscription. Plus, the internet was growing, and we also found some of our articles online. In those days, it was harder to shut down another website for infringing on your copyright.
But back to today’s report. One thing I did when I wrote my newsletter was address topics that no other writer would. There were deep dark secrets back in those days, and various interest groups didn’t want the great unwashed (that’s everyone except themselves) to know these things. So, I wrote about them in a column called “Balderdash.” Two of them have to do with today’s blog.
There were several myths about multi-pump pneumatics that were being espoused on the few chat forums we had back then. One was the myth that a multi-pump loses power when left to sit for a long time after pumping, because pumping generates heat (the heat of compression); and when the gun has the chance to cool off, it will slow down significantly.
Another myth was that the cadence at which you pump each stroke has a tremendous effect on the power output of the gun. I’m going to answer those myths right now.
I tested both questions, using my Sheridan Blue Streak and a Japanese-made Sharp Ace I owned and found that pumping the gun fast or slow had virtually no effect on velocity. There were differences, but they were smaller than the total variation of velocity both guns had, so the results were “in the noise,” as electronic engineers like to say. There was no difference in the velocities of the guns whether they were pumped slow or fast that could be supported with statistical confidence.
What about shooting immediately as opposed to waiting for a long time? Would velocity vary then? Many said that it would, because the heated reservoir (and the air inside) would have time to cool and therefore lose energy. W.H.B. Smith claimed in his classic book, Smith’s Standard Encyclopedia of Gas , Air and Spring Guns of the World, that there would be a difference from the loss of heat over time, but it would be very small. Back in 1995 when I ran this test, Smith’s book was one of the only books on the subject of air-gunnery in existence. We knew even then that there were errors in the book, such as the low results he got with the HW 54 EL Barakuda ether-injected rifle that was probably due to a blown piston seal. But since it was just about all there was, we read it and thought about it and this idea of power loss through cooling became a fact.
The test I ran with my Sharp Ace indicated a small difference in power that favored the hotter gun over the gun shot later, but the results were, once again, very close. At about 770 f.p.s., the two results were separated by just seven f.p.s. for 10 shots. I concluded that the difference might actually exist, but that it was too small to be of practical interest.
But let’s set those two questions aside now, because yesterday, blog reader Aaron prompted me to write this blog when he responded to my test of accuracy between the Ruger 10-22 and the AirForce Talon SS that wrote about in yesterday’s blog. Aaron said that he could not understand comparing airguns to powder burners. That each was created to do a different thing and that any comparison was therefore senseless (I’m using my own words to paraphrase his thoughts here).
I agree with Aaron that we shouldn’t compare airguns and firearms — except that so many people do. When I was growing up, I heard a lot of older boys and even men saying, “That old Benjamin of mine is as powerful as a .22. I just pump her up 30 times and she cracks like a rifle!”
Overlooking the fact that the gun they were talking about probably was a rifle, I understood what they meant and I’m sure you do, too. What they meant was their multi-pump, when pumped about 30 times, had (they assumed) all the velocity and (they assumed) power of a .22 rimfire cartridge.
At this point, blog reader twotalon chimed in to tell us he knew what the outcome of this test would be. Well, he was right, but there is a VERY important point that we all need to understand. While conducting the first test about the speed of the pump strokes affecting the velocity, the first time I ran the test I actually proved that it did! And I published the results that way!
Several people took exception to my findings, and at about the same time I was testing the Beeman R1 for the articles that would eventually become the R1 book. Well, I discovered that my ancient Shooting Chrony chronograph that I bought used from Paul Watts could be “tricked” into displaying velocities faster or slower, depending on the angle of the pellet path through the skyscreens. I had to throw out a lot of R1 test results after I found out how to “cheat” the machine by angling the barrel for the shot. And that made me wonder about everything else I had tested with the same machine, so Edith and I bit the bullet and I bought a new Oehler 35P chronograph.
The new chronograph showed that there was very little difference between slow and fast pumping, so I had to print a retraction to the earlier article. I also learned the value of good equipment, because I had to rerun a lot of the R1 tests that were already in the can.
I’m not saying anything bad about today’s Shooting Chrony chronographs. I use one most of the time these days. But the one I had been using for those tests was one of the very ancient ones that had cardboard “windows” above each skyscreen, and the ones on my machine had been so shot to pieces that the results were unreliable. You’d get a three-digit number, but how close it came to the truth was anyone’s guess.
Back to the report
At any rate, I’d always wondered if the old guys were kidding themselves by thinking an overpumped pneumatic was more powerful, so I conducted a test. I really didn’t want to pump my Blue Streak more than eight times because ever since it was brand new in 1978 I’d been so careful to limit my pumps to a maximum of eight, just like the manual advised.
I’m sure that I conducted that test and published the results somewhere, but I can’t find it anywhere in the index of the Airgun Letter. So, I had to run another test for you today. Once again, I drafted my 1978-vintage Blue Streak for the job. And we remember that the manual that I lost years ago, but which Pyramyd Air has in their online library of manuals, says that 8 pumps are the maximum. So, let’s roll!
For this test, I used my old Blue Streak, which I oiled especially for today. The pellets are all 14.3-grain .20-caliber Crosman Premiers.
Well, that chart shows what I was talking about, but not as well as I’d like. You can see the power drop off after the tenth pump stroke. But a Blue Streak should be doing that on pump number nine and the velocity should be much higher.
I could tell at pump five that my old Blue Streak wasn’t feeling well. It looks like the old gal finally needs some attention, because the last time I recorded the same pellet at 8 pumps it was going 643 f.p.s. and a few years before that it was close to 675. There’s reason No. 12 to own a chronograph.
Next, I pressed a Benjamin 392 into service. These days there isn’t much difference between the 392 and the Blue Streak, except for the caliber. My 392 is a pump-assist model that I reported on several years ago, but the powerplant is stock.
Same Crosman Premier 14.3-grain pellet was used, but this time in .22 caliber. Again, the gun was oiled before testing began.
That wasn’t the clear and obvious test result I was hoping for. In the past, I’ve seen velocities turn around after pump eight, or in some guns after pump nine and everything thereafter was slower. This time, the gun kept increasing until pump 13, where it went slower for the first time, but after that it seemed to want to remain at about the same velocity no matter how many pumps were put into the gun. This wasn’t from residual air pressure remaining in the reservoir, because I was dry-firing the rifle after each shot from seven pump strokes on. Usually, I’ll be able to hear when the gun hasn’t exhausted all its air because there will be a small crack from the dry-fire afterward, but that didn’t seem to be happening with either my Blue Streak or this 392. The Blue Streak just needs an overhaul but there could also be some dynamic about the pump-assist conversion I’m not familiar with, I guess.
But the main point I wanted to make today was that the gun doesn’t just keep on getting faster and faster with each additional pump stroke, and that was proven in both tests. So, the myth of 30 pump strokes turning it into a .22 rimfire is just that — a myth.
I’m not blaming Aaron for any of this. He only said he didn’t think we should compare airguns to firearms. He never mentioned any of these old stories, but that was enough to set me off on this strange quest to expose some old-wives’ tales about our airguns.
Now, I have yet another sick air rifle to care for. It seems that the cobbler’s children will have to go barefoot a while longer.