The Beemans are still telling airgunners that the BATF will come smashing down your door if you have a silencer on your airgun, but the BATF long ago sent out a letter affirming that a permanently attached silencer on a non-firearm- i.e., an airgun or paintball gun- is not a Class 3 weapon, and that it is the affixing of a device to a firearm that makes it a silencer. (Good thing, too, or they could cite everyone in possession of a small gasoline engine, since the mufflers attached to many could indeed meet the definition of a firearms silencer.) I did a post on this last year, I think, along with a facsimile image of the BATF letter and a cite of the regulations and commentary from the agency.
The people at Gamo have not been listening to the Beemans as they introduced not too long ago a rifle with a permanently attached silencer, the Gamo Whisperer. This gun has a fairly sophisticated multi-baffle silencer that is probably about as good as you’ll find on any air rifle, save for some of the really huge units seen on some pneumatic guns in England. And that brings up a good point: Exactly how effective is a silencer on an airgun?
Airguns have three sources of sound. One, the mechanical noise of the gun itself- sear breaking, piston moving, spring noise, etc. This doesn’t amount to all that much in most cases, although in a very quiet setting, a mechanically noisy gun can spook game. Second, the sound of the pellet. Again, not a terribly significant source of sound. Last, the sound of the compressed air exiting the barrel. IN a pneumatic gun, this can amount to a very loud pop- particularly in some of the big bore guns out there. In these guns, a silencer makes good sense. Most pellets travel at subsonic speeds and the sound of that air exiting the gun will reach game long before the pellet does.
Spring air guns expel a lot less air than do pneumatics, and most under 12 ft-lb guns are pretty quiet already. But when you get up to the 16-20 ft-lb range you start getting a pretty significant “pop” when you fire the gun. I’m not sure how much it spooks game, but it can be disturbing to your shooting partners- or so my friends tell me when I fired a Theoben Sirroco, which has a very sharp report, even with a simple muzzle brake/silencer permanently affixed to the barrel.
The Gamo Whisperer is billed as a “1200 fps” gun- a figure meaningless without knowing the pellet weight used to derive this figure, but if we assume a light 6 grain pellet, we’re just about up to 20 ft-lbs, and even an ultralight 5 grain pellet puts us at 16 ft-lbs. The Gamo people claim a “52% sound reduction” from their silencer- again, a rather meaningless number unless they tell us how it was derived. Sound pressure is measure logarithmically, and a 50% reduction is 3dB, which is not a halving in perceived sound intensity. Complicating things even more is the fact that you can’t simply measure the report of a gun using a standard sound pressure level meter; you need to do an impulse noise measurement.
All that aside, it’s nice to see Gamo make a solid effort at building a quieter airgun. Whether or not the “52%” figure is meaningful, I have no doubt that the device as described is sufficient to remove a lot of the sharpness of the report of the Whisperer.