If you have accuracy problems then try all the best pellets you can get. Sit comfortably (this is to try and eliminate human error) and do some five shot groups. You will get to know your gun and ammunition if you do a lot of 5 shot groups.
If the accuracy is poor then check that the:
Power is consistent. If the power is varying then Check tuning and correct lubrication.
If Power is not consistent, Check with a Good chronograph to make sure you have a consistent velocity over many shots.
Make sure Scope is not moving (especially Spring piston guns).
And Stock screws are tight.Tighten and use a thread locking compound if required.
Check the Barrel hinge pin is adjusted correctly (break barrel types). Some break barrel guns that are poorly made or badly designed can allow the jaws to widen. This will not affect the accuracy too much if you are using open sights, but will be very bad if you use a scope as the barrel can shut slightly off, compared to the scope mounted cylinder. This may only be a few thousandths of an inch. But at only ten yards it can be inches off.
Check that the A frames are tight if fitted.
The correct calibre. We had a customer who complained about poor accuracy. We changed and re-crowned three barrels before he brought it in and we found it to be accurate. It turned out he was using .177 pellets in a .22.
Spring piston type guns must not be rested or touching any solid object like a table or ledge. It will kick off the hard surface in any direction. You can rest on sandbags yourself but avoid direct gun contact, with any thing hard. Pre-charge, Co2, Pump up and single stroke pneumatic are not affected, this is why they are easier to shoot accurately. See how to fit and zero a scope on this site.
Poor Quality or badly made gun, this would be poor rifling and poor shot to shot consistency.
Repeaters? Try doing five shot groups by loading one pellet at a time, we have had some guns that are only accurate with one or two magazines. If the indexing of the mag is not perfect, then it will have poor accuracy.
Under levers with a tap! make sure the tap is exactly in line and made properly.
Poor quality pellets, or good ones that do not suit the gun. Even the best gun you can buy will shoot poorly with crap pellets.
Power is too high, this causes pellet distortion, this will get worse if you shorten the barrel and try to keep the power the same. The pellet can balloon out reducing the waist by forcing it outwards to the rifling. This is common once the power gets near 25 ft lbs.We do not recommend (FAC) power over this amount. This is only use full to impress your mates.
If you have the accuracy and 25 ft lbs, then this will kill small vermin out to around 80 yards without the danger of a rim-fire, that is dangerous to around a mile.
The FAC guns we sell are normally set to around 25 ft lbs or under unless specified differently by the customer. We recommend FAC guns to be set around this level for the best accuracy and number of shots. A 25 ft lbs air rifle has enough power to humanely dispatch rabbits at 80 yard.
Silencer fitting. (Pellet too close to side of silencer).
Poor quality telescopic sight, or damaged.
Parallax scope error.
Loose barrel or barrel bands.
Barrel needs cleaning.
We make an adjustable pellet sizer that can give you the extra accuracy. You can size the pellets down a little to get the correct size for the gun. It can be set for all the guns that you might have in that calibre. Loose pellets will fall in the sizer and tight ones will need more of a push, you will get the feel for it with use, you can then grade the pellets into A B or C. You would then only use the the best grade, that is not the pellet that falls in or is too tight.
Check the Trigger is not too hard to pull, some guns take over 8 lb. to pull the trigger. This is usually on poor quality guns. The better ones have an adjustable trigger. Do not set the trigger too light as it can be very dangerous. This is because it maybe OK after adjustment but after a little wear the gun can suddenly fire without warning. The best gun in the world is not much use with a hard or dodgy trigger.
Very high quality guns can be set very light down to a matter of ounces and still be safe unless your fingers are cold, and reduce your feel. Best to be on the safe side.
Check that the outside diameter of the barrel is dead centre, as on a great deal of guns they are often off centre. It might only be a few thousands of an inch but this is all it takes to affect the pellet hitting the inside of the silencer. I have shown an off centre barrel to give shooters an Idea of what can go wrong when you fit a silencer that just slides over the outside diameter of the barrel. Even when the barrel is centred quite good, and you cannot see that it is off centre, this does not mean it is in the centre. It might only be a few thousandth’s of an inch out, but by the time you extend this out to about six or seven inches, you can be a long way out causing the pellet to be too close to one side and maybe even striking the side of the silencer. This will obviously ruin any accuracy that the barrel had.
Silencers or adaptors that lock on with a grub screw usually make the problem a lot worse by pulling the adaptor over to one side.
A barrel is screw cut by locating on the bore and the outside turned down to size while using a live centre in the barrel bore. This ensures that the outside is concentric to the bore. This can only be done when the barrel is larger than the thread required.A standard silencer thread for Air rifles and rim-fire rifles is 1/2 inch X 20TPI Male.
If the A Frame off to one side will not really cause bad accuracy, but will cause problems when you try to zero the scope. That is if the A Frame is over to the left, then the gun will group well over to the left and you may not be able to zero the scope. The adjustment on the scope will only allow a limited amount of movement to zero the scope.
I usually fill a pre charge gun to the recommended pressure, then fire through a good chrono, writing it down every shot until the power drops off. Then the written figures can be put in the computer. You can then create charts and graphs, this will give you the power curve for that gun. Then when you go shooting, if the gun does 80 consistent shots, then just put 70 to 80 pellets in your pellet pouch, to make sure you don’t run out of air pressure (or Co2) when hunting. When your pouch is empty you know it is time to re charge the reservoir. This is recommended for the QB 78 Co2 rifles. Fill the gun with new Co2 capsules and fire through a chronograph until the power drops off. If the power starts to drop off after say 40 shots then I would put 35pellets in my pellet pouch (or pocket). Then when my pellets have been used, I know it is time to exhaust the rest of the gas and start again. This will prevent you forgetting that your pressure could be running too low and wounding the quarry.