Shrouded Barrels and Moderators on Airguns
Jim Chapman
I have enumerated the advantages of airguns many times , and they are more or less in line with what I hear from the growing numbers using airguns for hunting and pest control. While each individualís priorities may vary, one consistently stated advantage is that airguns are quiet. Depending on the type of gun and how it is configured, the sound signature is typically far less than even a .22 subsonic rimfire.

Airguns are quieter than firearms, regardless of the power plant used. However, not all airguns generate the same type or intensity of sound; the sound generated from a spring piston airgun is at least partially of mechanical origin related to the spring piston slamming home, these guns generate a relatively small volume of air to drive the pellet forward making them the quietest of the airgun power plants. The release of a much larger volume of compressed air from a PCP generates a louder discharge sound that is closer to a firearm, though not exactly the same or as loud. Many airguns generate velocities in the subsonic range, but at higher velocities (around 1100 fps) a supersonic ďcrackĒ will be noted. Even in those guns with the potential of going supersonic, the savvy shooter will often dial down the power setting or use a heavier pellet to achieve optimal ballistic performance at lower velocities along with a concurrent reduction in the sound signature.

Beyond the intrinsically quieter discharge of airguns, they may be further suppressed to a level that is truly amazing by either using a silencer or a shrouded barrel. Before entering this discussion there are a couple of legal issues worth having a look at. A silencer that can be used, or modified for use on a firearm comes under the jurisdiction of the BATF. It is considered a firearm and must carry a serial number; furthermore legal possession requires a federal permit. Unlike the right to own a firearm, there is not a constitutional right to own a silencer and not all states allow their citizens to possess one under any circumstance. This license may or may not be difficult to obtain depending on where you live, and it will take a bit of time, effort, and a couple hundred bucks regardless. If the airgun silencer and its parts can not be used or modified for use on a firearm, then it should fall outside of the jurisdiction of BATF and not require the license. Many airgunners believe that an air rifle with a moderator (silencer) permanently attached is therefore legal. This is somewhat of a gray zone and the BATF in my experience, does not always have a consistent interpretation of their own regulations and guidelines. For shooters outside of the USA, there are many airgun companies that supply silencers as options and third party manufacturers offering a range of aftermarket products. It is odd that in countries such as the UK and South Africa that have laws which are more restrictive overall, the use of an airgun silencer is considered an almost essential piece of equipment. You cannot buy these after market products here for the aforementioned reasons, though there are a few rifle models available that have a permanently attached silencer which are imported and sold domestically. There are at least a couple of companies looking at the manufacture of airgun silencers from materials that would disintegrate under the temperatures and pressures generated by a firearm, but to my knowledge this is still in the early R&D phase and I donít know if the BATF will accept them as a work-around. I would not recommend using an after market silencer on your airgun in the States without the appropriate license, itís not worth the risk.

A developing trend that provides a very quiet gun while fulfilling both the letter and the spirit of the law, are airguns with integrated barrel shrouds. These are full length shrouds that are built into the gun and provide a gas porting function without an extraneous ďdeviceĒ, and are an integrated component of the airgun. These are very effective in reducing a PCP rifles sound signature, with the added advantage of not substantially increasing the guns overall length. There is an increasing trend by most of the high end gun makers to offer models with integrated shrouds

In addition to the legal possession of devices used to silence airguns, you also need to consider local hunting regulations. Some states do not allow silenced guns for hunting, some do not allow taking game animals but are OK for non-game animals, and pest control activities usually get pretty wide latitude. But be smart and check, donít get yourself in trouble and your gun confiscated!

OK, so once you get these details out of the way, how do moderated guns work in the field? Two of the outstanding hunting rifles Iíve been using for several months are the AirArms S410 FAC, and the Rohm Twinmaster Air Hunter Carbine, both .22 caliber and both shrouded. These guns are more than capable of ľĒ 50 yard groups, and can reach out much further with the power to anchor small game while generating a sound only a little louder than snapping your fingers. On jackrabbits, prairie dogs, and ground squirrel shoots, Iíve knocked multiple varmints over without disturbing their neighbor sitting a foot away. Doing pest control duty on a friendís farm in South Africa that was literally buried under a variety of pigeon species raiding the feeders; we sat in camo quietly picking off multitudes of birds without giving away our position. The advantage of these quiet airarms for urban predator and pest control duties are obvious, and opens up more shooting opportunity for those that might not otherwise be able to participate in the sport.

The majority of airguns I use when shooting and hunting outside of the USA are silenced, and I find this especially useful when hunting in more densely populated regions or around livestock. I have a couple of airgun silencers that I leave with friends in South Africa and attach to my rifles whenever we head out for pest control around the farm. The places I hunt small game here at home arenít generally that noise sensitive, but places where I shoot pest often are. I like the fact that using a gun with an integrated shroud I can be positioned in a field near a factory building with people less than a hundred yards from me, and not be heard. There is also a lot to be said for shooting moderated guns in my basement range as well, the family can be watching TV or reading upstairs and I donít disturb anyone, plus I donít need to wear hearing protection. I think that if you are looking for a pest control gun or will be shooting in a noise sensitive area, it would be well worth looking for one with a fully shrouded barrel. If you will be using it to hunt small game, just make sure of your local regulations. With no felt recoil from the rifle, it is an awesome experience to shoot a prairie dog at 75 yards and watch him through the scope silently flipping off the mound!
Shrouded barrel on left and a threaded propriatry moderator (right).
Disassembled moderator showing the baffles which are the primary components in redirecting air from behimd the pellet
Three methods of attaching a moderator; propriatary threaded attachment on moderator,(L), standard fitting for threaded barrel (C), and slip on moderator attached by tightening allen screws (R).
The three type of attachments being deployed
The Evanix Blizzard with an integrated shrouded barrel effectively reduces the discharge to a low level sound, and adds minimally to the overall length of the rifle.