Accuracy in Spring Airguns

Getting maximum accuracy from spring airguns requires attention to two areas: The gun itself, and your shooting position. Let’s address the gun first.

Assuming you have a new spring air rifle, the first thing you should do is insure that all the screws are tight- with one exception that we’ll get to in a minute. In a break barrel gun there will be a pivot screw that should be snugged up, and perhaps treated with a drop of purple (low strength) Loctite. The screws that fasten the stock to the action should be snugged up as well, with the exception of the front screw on the trigger guard of HW rifles- which includes a number of Beeman-labeled guns, like the R10, R11, R8, R7, etc. Over-tightening this screw will prevent the gun from firing.

Assuming that your gun is now snugged up, with no loose bits, and you’re standing in front of your pellet trap or target backstop, the next step is to cock it and insert a pellet in the breech. For maximum accuracy, pellets should be seated just flush with the rear of the breech. If you bought one of those Beeman pellet seating tools designed to push the pellet further into the breech- don’t do it. The pellet should be as close to the transfer port as possible for maximum power and accuracy, as many tests have verified.
Now you’re ready to fire. But first, look at how you’re holding the gun. For maximum accuracy, spring guns should be supported as lightly as possible. Rest the forearm of the rifle on your palm or arm, and don’t pull the butt end back to your shoulder, as you might do with a high-power rifle. Just let it lie there.

Now close your eyes, find a stable, comfortable shooting position, and open your eyes. If the sights or the scope are pointed at the target, great. If not, don’t move the rifle around to aim- move your body. It’s important to be able to shoot from a relaxed position. More on this in later articles.

Okay. On target? Relaxed position? Listen to your heart beat. Every time it does, the crosshairs might jump a tiny bit. You want to shoot between the bumps. Place the pad at the tip of your index finger on the trigger. If it’s a two-stage trigger, take up the slack. Now slowlyly increase pressure on the trigger, until… pop. Bullseye.

Lead Free Pellets

Increasingly shooters around the world- at least where gun ownership is allowed- are being pushed into using lead-free projectiles. This began with shotgunners, and perhaps reasonably so, as shotgunning dumps more lead into the environment, and over a wider area, than any other shooting sport. A round of sporting clays might result in dumping 100 1oz loads of lead over a wide area- that’s 43,750 grains, or the equivalent of 5,538 Crosman .177 7.9gr Premier pellets. And the lead from that shotgun isn’t deposited in a backstop- or a game animal but is finely distributed over a wide area.

That brings up a big question: Is lead pollution from pellet rifles really a problem? Compared to shotguns, obviously not. It’s easy to collect all the spent pellets from formal target shooting. A day’s hunting might result in a dozen misses- worst case, 200 grains of heavy .22 caliber pellets. That’s less than one shot from a .410 shotgun. A careful airgun hunter probably won’t have more than one or two misses.

But let’s assume that we want to be extra careful, and make sure we don’t dump any lead, period. So what are our options?

There are a number of lead free pellets on the market now. All use a lead-free alloy. Some are bore fitting, and others, like the Prometheus pellets that have been around since the 90s, use a plastic sabot- which brings up the question of scattering all these non-biodegradable plastic sabots about on every shot, but never mind that for now. How well do the lead free pellets perform?

Lead free pellets are typically made from a tin, aluminum and zinc alloys, these being relatively cheap as well as easy to cast and machine, But they’re also significantly lighter than lead, and that causes problems; modern airguns typically achieve maximum power and accuracy from heavier pellets than are generally available in non-lead formulations, and that results not only in loss of accuracy and efficiency, but in the case of high-powered spring guns, damage as well, as the light pellets don’t offer enough resistance to the spring and piston.

Since the diameter of the barrel limits how big you can make pellets in that dimension, the only way to increase mass is to use a heavier element or a longer pellets. Longer pellets need a much high rate of barrel twist to be stabilized in flight, so that’s not a good solution for existing guns. Are there heavier elements? Yes, though most are either too expensive or have other undesirable properties. Bismuth does come to mind, as shotgunners are using it, but it’s very soft, significantly more expensive than lead, and recently there have been studies published on toxic effects of bismuth pellets ingested by animals as well- so that’s no long term solution. (See this paper, for example).

I do suspect that there may be lead-free pellets in our future- but not with the present technology.

The Combustion Myth

Back in the 1950s the father and son team of G. V. Cardew and G. M. Cardew published the results of an interesting study in which that proposed that a large part of the power of airguns came from the combustion of lubricants in the compression chamber of spring-air guns. Thier experiment was simple, and convincing: They fired a .22 cal Weihrauch HW 35 that had been purged of air and filled with nitrogen. Muzzle velocities obtained were significantly lower than when the gun was fired in air.

I’ve always been somewhat distrustful of the Cardews’ experimental methodology, which involved placing a gun in a plastic bag, pumping out air, and bleeding in nitrogen, and then opening the bag and firing the gun, but I’m willing to believe it worked, and that they obtained the results they published. Certainly these guns were burning part of their lubricant; anyone who’s owned a Daisy BB gun is familair with the wisp of smoke and the smell of burning oil that follows a shot from a well-oiled gun.
The airguns of the Cardews’ era had leather piston seals which had to be fairly well saturated with lubricant in order to provide a good seal. Some of this oil would invariably be sprayed into the barrel in the form of a very fine aerosol on firing, and that aerosol would in turn be ignited by the hot air coming through the transfer port, and that would add to the propulsive power of the gun.

But there would also be lubricant burning in the compression chamber- and that should interfere with propulsion, by setting up a shock wave that would drive the piston back before maximum pressure was built up in the barrel. I have, on a number of occasions, encountered just such a situation in guns in which some combustible material- usually a pellet lube or cleaning solvent- has gotten into the chamber. The result is usually a loud report, a blackened (and sometimes ruined) piston seal, often a damaged mainspring, and a drop in muzzle velocity.
And there’s another issue. But in the 1960s, Ladd Fanta started experimenting with using silicone oils- which do not burn- in place of the combustible hydrocarbon oils traditionally used in air guns. Airgun dealer Robert Law also began promoting the use of these new lubricants. And looking over some of the catalogs that Law produced back then, no where does he mention any loss of velocity from using silicone based lubricants. So I remain- let’s say- skeptical, but open to being convinced.

Whether or not the Cardews’ test showed what was claimed, the results still have no applicability for today’s guns. Modern airguns- which the possible exception of some of the very cheapest Chinese guns still sitting in a warehouse somewhere- don’t use leather seals. Any lube beyond a fraction of a gram is quickly shot out. Modern synthetic lubes are made of silicone- a tightly bonded silicon-oxygen molecule that simply will not burn. And despite using only a miniscule amount of lubrication, and being fired regularly for years or decades without any additional lubricant, today’s spring airguns commonly achieve muzzle energies and velocities unheard of in the Cardews’ time.