Monday, October 31, 2011
What’s the difference between a moderator and a silencer and do we really need them? Matt Clark finds out.
To some people it might seem strange that you would need a silencer for an air rifle. After all, unlike firearms or shotguns, theres no explosion when you pull the trigger. So whats the point of having a silencer?
If youve ever stood next to someone firing a springer or PCP you will hear a sharp crack from the muzzle. Thats the compressed air expanding after it has pushed the pellet out of the barrel. This can disturb the quarry youve been so careful to stalk, or if you are shooting in your backyard, it can disturb your neighbours. Both these scenarios can be avoided by fitting a silencer to you airgun.
Silencers are also called moderators. This is because the cylindrical device that many airgunners fit to their rifle barrels moderates the sound, rather than totally silencing it. Its true to say that some moderators do a better job than others.
For example, precharged airguns can be more effectively moderated than spring- powered airguns. Thats because most of the power developed by the action on a PCP is a small tink of the valve opening and closing. The noisy part comes when the compressed air leaves the barrel, but its relatively easy to damp this down.
A spring gun has all the commotion of the spring expanding and crashing into the end wall of the compression chamber. It produces a medley of sound similar to a drunk staggering home through a junk yard. The only way to lessen this calamitous racket is to take your springer to a skilled gunsmith who will polish and tweak the internals to make them smoother; or buying a springer with synthetic bearings like the Air Arms Pro-Sport or Weihrauch HW97.
You would be forgiven for thinking its only worth silencing a PCP because the noise of the internals of a springer will give the game away even if you had a moderator fitted to the end of your barrel. But what the shooter hears when he or she takes a shot is not what your quarry hears. A rabbit busy munching grass will only hear the twangs of a springer as something distant and unthreatening. The first thing he will know about your shot - if your springer is moderated - is when the pellet hits The Moderator home. Thats because the sound behind the pellet will have been muted by the moderator.
The moderator can also make the sound directional. This is why after knocking one rabbit down another rabbit quite close by you can often take a shot at another. Apart form his mates weird break dancing, the other rabbit will be blissfully unaware of your presence because the sound of the shot was channelled so specifically to the target.
So are moderators only of use to hunters? No. Backyard airgunners can benefit from them as well because muted shots are less likely to disturb their neighbours. In competition noisy rifle reports can disturb competitors, leading to unnecessary friction, so all airgunners can benefit from moderators.
There are plenty of moderators to choose from. Some are just a chamber where the air behind the pellet is allowed to expand before exiting the muzzle, thus reducing the crack. More effective ones use a series of baffles, which can be purpose-shaped metal, and plastic. One renowned silencer uses a hair curler. These baffles grab small quantities of excess air until the air behind the pellet emerges from the barrel with the wind knocked out of it.
Whatever type and size of silencer you use make sure its a perfect fit over the muzzle and is in perfect alignment with the bore of the barrel. If the muzzle of your airgun is not already threaded, a screw on silencer is best fitted by a gunsmith, but simpler sleeve-fit designs can just slide on to the barrel and be fixed in place by tightening a grub screw. Its always best to fit a silencer before you go to the trouble of zeroing your rifle because the moderator can have a very slight effect on velocity and also trajectory of your pellet, which can push your zero out.
The only down side of a silencer is that it can make your rifle rather long and unwieldy and this would explain the move towards carbines in recent times. However, companies like Daystate have started to develop new silencers, like the Airstream. It has some of its volume in front of the barrel and some overlapping it, which means the total volume of sound moderation is large, but because part of it fits over the barrel, it is shorter and less likely to unbalance the rifle.
A silencer is a basic, but essential bit of kit for both hunters and back yard plinkers and they dont have to cost the earth. Prices are around 30 upwards, but because of the Violent Crime Reduction Act silencers can no longer be sold through the post, but must be bought in person.