This story was originally published in the June 2017 edition of the SSAA’s Australian Shooter magazine.
Like any rifle, an air rifle requires some tuning to get the most out of it. First and foremost is accuracy. If you want to extract the full potential of your air rifle for plinking, target practice and hunting then it needs to be as accurate as it can be. There is a range of relatively simple things that can improve the accuracy of an air rifle.
Having bought a brand new spring powered Weihrauch HW 97K air rifle I fitted the old scope that had been on the Diana 34 for many years. The first thing I discovered was that I had to crank the scope elevation right down, almost to the limits of its adjustment to get the rifle to shoot on point of aim at 30 metres. I did not realise it just then, but that was a significant issue in itself.
The next problem surfaced immediately. The grouping was terrible! The obvious problem was my scope. It had seen many years of service on the Diana 34 and the deteriorating accuracy, which I had blamed on the Diana, was now obviously a loose reticule. So, I did some homework and set about finding an appropriate scope for the 97K.
In doing that, I found that proper scope selection is critical on powerful springer air rifles. Springer air rifles have a jarring to-fro recoil that most scopes cannot handle. It is the forward recoil that does the damage. Most scopes are designed for use on centrefire rifles where there is only the reverse recoil. You can take a quality scope that has functioned flawlessly on a big magnum rifle for years, put it on a big springer air rifle and destroy the reticule in no time.
In selecting a scope for a springer air rifle you must choose one that is built and rated for use on such rifles. There are a number of manufacturers who manufacture air rifle specific scopes. The other advantage of choosing an air rifle rated scope, apart from the reticule design, is in the focus distance. Air rifle scopes are designed to have a focus that is parallax free at about 30 to 40 metres – the typical shooting range of an air rifle. Scopes intended for use on cartridge rifles generally have their parallax set in the 100 to 150 metre range. Obviously, accuracy is best when the rifle is used at, or close to, the parallax-free distance of the scope.
I did some research and made a decision. A new, air rifle rated Bushnell 4-12×40 AO XLT Trophy scope was fitted to the 97K and zeroed in. Once again I found that I had to crank the elevation way down to get the rifle on target. Pleasingly, group sizes were much better. Problem solved, or so I thought. Over a period of about six months I detected deterioration in accuracy.
There followed a period of great frustration as I sought to get the rifle shooting to its capabilities. I searched the air rifle forums on the internet and sought out more experienced air rifle shooters for advice. The next step in my learning was when I became aware of barrel droop in air rifles and the importance of correcting for that with appropriate, adjustable mounts.
ADJUSTABLE SCOPE MOUNTS & BARREL DROOP
I dismissed barrel droop initially because I wrongly assumed it was something that would only be an issue on well used break action air rifles. I forget who put me straight on that, but it turned out to be one of the steps in the right direction.
So what is barrel droop? It relates to the axes of the rifle’s bore and the centreline of the scope sight. Generally, with centrefire rifles the barrel bore is angled upwards and passes through the centreline of the scope sight. Relatively few scope adjustments are required to get the scope on target.
Most air rifles, for reasons I never discovered, have a situation where the barrel axis and the centreline of the scope actually diverge. That is, having mounted your scope to the air rifle, the barrel actually points down and away from the scope centreline, not up and through it as on a centrefire rifle. That situation is barrel droop.
The scope needs a lot more elevation adjustment to get it on target. You will often find that you are right out near the limits of adjustable elevation to get the scope on target. Now, that is where the problem kicks in.
The mechanism that moves the reticule within the scope tube, being near its limits and subject to the brutal recoil of the spring powered air rifle, moves slightly at the shot and does not return exactly to its set position after a shot. This alone can be the source of poor group sizes in big springers.
Initially I tried just shimming the rear scope ring. It worked, but I was shocked at how much shimming was needed and also concerned at the stresses I was putting on the scope. That led me to following up on a strongly recommended suggestion and buying a Sportsmatch AOP55 adjustable scope mount for my 97K.
I dialled my scope back to dead centre, making sure the vertical and horizontal adjustments were equidistant from their limits of movement. Then I fitted the scope securely in the adjustable mount rings and began a process of fitting the scope mount to rifle and shooting a group, then removing the scope and mount to adjust the mounting. There were clear instructions with the AOP55 adjustable mount for that and it ended up being a fairly quick and painless procedure.
Once I had the adjusted the mounts to have the rifle shooting within 50mm of the point of aim at 30 metres I then made the relatively few adjustments on the scope itself to bring it dead on target. Being in the centre of its adjustment range the scope from then on returned exactly to its set position with each shot and group size was much improved. That problem was now solved!
PELLET SELECTION AND TESTING
It is surprising how much variation in accuracy there can be between different types of air rifle pellets in any given air rifle. Therefore, one essential for any air gunner keen to get the best from their rifle is to test a range of pellets. H&N produce a convenient sample pack with a range of their pellets for testing. It is a pity more air rifle pellet manufacturers do not do the same. The only other way to get samples for testing is to ask around other air rifle shooters and obtain samples of 20 to 30 pellets of different makes for testing.
A steady rest and good shooting technique (see below) on a calm day is a prerequisite for serious testing. Shoot a few five shot groups and measure the average group size. The range over which you shoot should ideally be around 20 to 30 metres, which pretty much equates to your hunting range. My maximum hunting range is determined by my ability to keep the group under 20 cent piece size. As in centrefire rifle hunting, your maximum hunting distance is determined by your ability to consistently keep your shots within the kill zone of your quarry, irrespective of the velocity and trajectory of your rifle.
If you have a particularly accurate air rifle that may well be out to 50 or 60 metres. If your rifle and pellet combination is not so accurate the maximum hunting range could drop back to 10 to 20 metres. That is not necessarily a problem either. For shooting rats, pigeons and mynas in farm sheds, where I am shooting only to about 10 metres, I like to use the hard-hitting H&N Crow Magnum 18.2 grain hollow points. These pellets generally expand by around 40% on impact and are ideal for whacking pests inside sheds. They do not group as well at 30 metres as the H&N FTT pellets I generally use, but their close range accuracy inside a shed is not an issue.
Contrary to common opinion, regular cleaning of an air rifle’s barrel is necessary for maintaining accuracy. At the very least, the easy option of simply firing a couple of fibre cleaning wads through the barrel after every 50 shots is a good start. These wads are best fired with a normal pellet behind them. A cleaning wad by itself in the barrel does not provide anywhere near the resistance that a pellet does and you run the risk of damaging the rifle’s piston seals by firing cleaning wads by themselves.
If the rifle accuracy starts to deteriorate, the first thing to do is to clean the barrel more thoroughly. Air gunners tend to opt for pull-through and patches for this in preference to a cleaning rod. This is particularly true for fixed barrel air rifles where the rod would have to be pushed down the barrel toward the piston, with the risk of damaging the port seal between the piston and barrel.
For cleaning the bore a couple of patches wet with Remoil, or similar, should be pulled through and discarded, followed by a dry patch. Repeat if necessary until the patches emerge clean. In doing that the crown of the muzzle should be protected from abrasion by the pull through line. In .22 calibre air rifles a drinking straw makes an excellent improvised muzzle guide.
Regular use of fibre wads and occasional patching with Remoil is normally all that is required to keep the air rifle bore clean and accurate. Only in extreme cases of neglect may more aggressive solvents be required to shift accumulated lead fouling.
Whenever using oils or solvents it is important to prevent any liquid entering the piston chamber. Placing a small wad of cloth, or some other simple barrier is generally sufficient to protect against that.
FOLLOW THROUGH & THE ARTILLERY HOLD
Springer air rifles require a bit more finesse in firing than do cartridge rifles. Follow through is a good habit when shooting any rifle, especially so for an air rifle. While it is imperceptible to the shooter, when comparing cartridge and air rifles there is a significant difference in the time between when the trigger is released and the projectile leaves the barrel. That time is slower in air rifles and requires the shooter to practice a more pronounced follow through when shooting a springer. Follow through is maintaining your hold and sight picture for a distinct moment after the shot is taken. You might get away with lifting your head up on firing a cartridge rifle, but doing so on an air rifle will more than likely lead to an accuracy problem.
Accuracy in springer air rifles is also improved by adopting a particular holding technique. Known as the artillery hold, the rifle is not held as tightly to the shoulder as a cartridge rifle. It is important to let the rifle recoil as freely as possible, not unlike what is seen when an artillery piece is fired, hence the name.
Adopting both good follow through and the artillery hold is another way of improving accuracy in your air rifle.