Posts Tagged ‘testing’

For years, I have heard things like “spring-pistons don’t like heavy pellets” and “CO2, pre-charged pneumatics and pump guns are more efficient with heavy pellets.” I guess I just accepted these truths as an article of faith and never really thought much more about them.

But recently I have been testing several .25 caliber – quarterbore – air rifles, and the tale that the chronograph tells is interesting. Put simply, when it comes to power generation – that is, foot-pounds measured at the muzzle – springers tend to like light pellets and pneumatics prefer heavier pellets. Of course, it isn’t always a straight linear function, because there are other variables, such as how tightly the pellet fits in the bore.

It all started when I was chronographing a trio of break barrel .25 cal. springers. I was using Gamo Pro Magnum 21.91 gr. pellets to chronograph them, because I had a plentiful supply of those pellets. One of the rifles was slinging the Gamo pellets at 565 fps average, which works out to 15.53 foot-pounds average. I mentioned this to the importer, and he suggested trying JSB Kings (25.4 gr.). Somewhat counter to the “law” about springers, the heavier pellet did better in terms of power but slightly worse in velocity: the JSB Kings averaged 555 fps for 17.37 foot-pounds at the muzzle. But the real surprise came with the lightest pellet. 19 gr. Milbro Rhino pellets rocketed through the traps at 667 fps for a sparkling 18.7 foot-pounds. In this case, the law about springers proved right: the lightest pellet did generate the most power in this .25 cal. spring-piston powerplant.

Okay, I thought, but what about the pneumatic airguns, do they obey the “rules” or not? It was raining when I thought about answering this question, and I usually need to do my chronographing outdoors, so I turned to the respected varminter Cliff Tharpe. Cliff, whose online handle is VarmintAir, is producer of the Airgun Hunting the California Ground Squirrel DVD. He has deep experience in hunting and clobbering vermin with air rifles.

Cliff has a factory stock .25 Benjamin Marauder that he routinely uses to pop prairie dogs at 50-100 yards. He sent me some data on his experience chronographing different weight pellets through the Marauder, with the following note: “These were all shot at the factory settings, whatever those may be.  All velocities were taken with the start screen 12 inches from the muzzle.  I use a CED M2 Chronograph set up indoors, with the infrared screens.  Two mags, for sixteen shots with each pellet.  All pellets were weight sorted.  This is with a 3000 psi fill. “

And here’s the data:

  • JSB .25 Quarter Bore, 25.4 grain – avg. vel. – 881 fps – fpe 43.8
  • Benjamin .25 dome head, 27.8 grain – avg. vel. – 845 fps – fpe 44
  • Beeman Kodiak .25, 30.8 grain – avg. vel. – 821 fps – fpe 46.1

Here we have a straight linear relationship – the heavier the pellet, the lower the velocity, and the greater the power that is generated.

Now, having said all that, what’s the most important thing?

Accuracy, of course. A firearms expert once said, “A hit with a .22 beats a clean miss with a .45.” And he was right. If you can’t reliably hit what you’re aiming at, it doesn’t matter how much power you are generating. The first thing you need is sufficient accuracy to hit your intended target at the range at which you plan to shoot. If you are planning to hunt, once you have the accuracy, then you need sufficient power to humanely take whatever game you are after.

Til next time, aim true and shoot straight.

– Jock Elliott