Inaccuracy in Airgunsby Lewis Reinhold
Reprinted from the Beeman Precision Airgun Guide
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Frequently my phone conversations concerns the customer's airgun which "can't hit the broad side of a barn." Invariably, the frustrated owner has "tried everything, but it still won't group no matter what!" Unfortunately, the information supplied with most new airguns is fairly ordinary at best and won't offer much assistance, so here is a list of the frequent problem areas to look at before you give up in despair. Most of the information applies to conventional spring piston airguns but is appropriate to other systems as well.
Loose Stock Screws are probably the most common cause of inaccuracy in airguns. Even a quarter turn loose can translate to 50mm difference at 25 meters. Most airguns have three blade or Phillips head screws securing the action to the stock - two in the forearm and one through the trigger guard. These must be firmly tight at all times with any lock washers in place. Loose screws on the breech-block assembly will also affect accuracy on break-barrel models.
CAUTION! Before you stampede to your tool box - airguns, just like regular firearm slotted screws, are different. They require special screwdrivers with parallel tapers unlike carpentry screws. Use a regular screwdriver and you risk damaging the screwhead, the gun and yourself sometimes irreparably! We (Beeman) offer the handy and compact Gunsmith Screwdriver Kit that covers most of the screws you will encounter on your airguns including Phillips heads. Don't overtighten! Any more tension than firm will probably compress the wood and destroy the stock, particularly in the forearm.
Loose Sights. Open sights - check that the front sight attachment screw is tight and the sight element held within is secure. Check the rear sight for play and tightness on the breech block. Scope Mounts - Any old scope mount just won't do on any airgun! On magnum and beyond sporters, you must use a scope mount specifically designed for airgun use. These may have an integral cope stop pin that located in special arrestor holes milled into the receivers of the best sporters. Spring piston airguns don't just recoil backwards, they snap forward too and coupled with the vibration of the mainspring will continually drive a less than proper mount off the scope grooves. Separate scope stops are also available for the same purpose. Scopes can also move through the scope rings but this problem is usually eliminated using the right scope mount.
Using a Regular Firearm Scope. Leave your old .22 scope on your old .22! If you are serious about your airgunning and want the best performance our of your airgun, you must use a scope specifically designed for airgun use.
Don't get conned or laughed off at your local gun shop! Today's magnum spring piston and gas spring airguns will promptly break a less than proper airgun scope. As mentioned previously, airguns recoil backwards then snap forward; this is what destroys regular scopes. Proper airgun scopes have their lenses and reticule braced at the front and the back whereas most regular firearm scopes are only braced at the rear. This double recoil peculiar to airguns, coupled with the vibration of the mainspring, will quickly destroy even the biggest brand names in scopes.
Secondly, airguns shoot at shorter distances than regular firearms, and finally most regular firearm scopes are parallax corrected to 50 yards or more. Proper airguns scopes have an externally adjustable parallax ring on the objective or front end to focus clearly at all distances down to about 10 meters. This can also be used as a range finder to estimate distances to your target. Simply turn the parallax adjusting ring until you get the most clear picture possible and read the number on the ring. Finally, airguns have a much more pronounced trajectory than firearms and proper airgun scopes have and elevation bias so there is more up than down adjustment, eliminating the need to shim the scope mount and possibly crush or bend the scope tube.
Incorrect Barrel Tension. Barrel cocking airguns must have the pivot tension set carefully. Too much and the barrel detent will not consistently lock up and there will be galling of the breech block. Too little and there will be blow by at the breech. Both situations will cause wild and erratic groups. The correct tension is the point where the barrel will just stay anywhere on the return arc after cocking. Better barrel cocking airguns have adjustable pivot tension.
You must use proper gunsmith screwdrivers, keep your finger out of the trigger guard and don't adjust a cocked gun! On Beeman R series, Weihrauch and FWB sport, loosen the right hand side screw/nut and tighten the left hand side bolt. When the tension is correct, tighten the nut against the bolt and recheck. On Diana, Anschutz and others remove the small lock screw and tighten the pivot bolt to a compromise position that allows the lock screw to locate into one of the cutouts in the pivot bolt head.
The Wrong Pellet. Most inaccuracy queries eminate from owners of .177 magnum sporters capable of muzzle velocities in excess of 1000 fpt. In the power race, many manufacturers use the very lightest pellet available to achieve their advertised velocity and boost their sales. Invariable, this pellet is not the best for these guns, in terms of accuracy, energy and velocity retention downrange. For magnum air rifles capable of 1000+ fpt, avoid using any pellet lighter than 8.0 grain. Shooting these pellets could result in a supersonic muzzle velocity and then a drop to subsonic later during the flight, the shock of which will cause a violent tumbling and therefor leads to inaccuracy. Every gun is different and what works for one gun doesn't mean it will work on the next gun even if it is the same make and model.
Buy an assortment pack in your caliber, and see which pellets shoot the best group at your preferred shooting distance. Pellet induced accuracy problems on lower powered airguns can usually be cured by switching brands or types. Don't use old and oxidized pellets or any deformed example - discard them immediately. Only use high quality lead pellets from respected manufacturers. Cheap pellets are false economy.
Dirty Bore. Airguns do foul barrels but not in the same manner as regular minute traces of lead and the gun's mechanisms spray lubricants from the compression chamber that deposit in the rifling. This must be carefully removed with a proper airgun barrel cleaning kit. We strongly recommend the Beeman Zip Cleaning Kit which is a compact flexible rod that won't damage the delicate crown or rifling and it covers all four calibers. Carefully follow the directions for the best results.
Don't use regular firearm solvents because they will attack the seals. Use a gentle degreaser on a pure cotton patch and make sure the bore is dry before applying a very light coat of polarizing oil to protect against rust. A good quick fix in the field is to use "Quick Clean" felt pellets which are fired though the barrel every 1000 shots or so. On any airgun with greater than match velocity, use multiple (two on pistols, three+ on rifles) Quick Clean pellets. Always sight in your airgun each time you open a new tin of pellets. Variations can occur between batches.
Incorrect Shooting Techniques. Regular firearm dogma doesn't work on spring piston and gas spring airguns. That is why many expert firearm marksmen can't shoot airguns accurately and why many expert airgunners shoot regular firearms so well. There are two basic reasons:
A. Hold your airgun loosely against your shoulder and let it jump around when you fire it. Don't pull it in hard into your shoulder or strangle its forearm and don't rest the forearm on a hard surface. Let it recoil and vibrate freely - don't try to prevent it.
B. When you sense that your airgun has fired, the pellet is only just starting up the barrel. The lock time is so much slower on airguns compared to firearms so you have to adjust and follow through. Hang onto your sight picture just a little longer and your groups will shrink.
Naturally, trigger, breathing and stance principles still apply and there are plenty of books available on these topics to consult. If you have followed all these suggestions and still have accuracy problems your airgun may need the attention of an airgunsmith.
Don't even attempt to disassemble your airgun - this will void your warranty! From experience it is far cheaper in the end to have an airgun specialist attend to it.
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