The label on the ammo box says subsonic, so this stuff won’t spook every deer in the county like your earth-shattering .30-06 does, right? Well, sort of. Subsonic cartridges do produce less noise than full-velocity rounds, but there’s no free lunch—as usual. Your rifle will still go bang, and none of this quieter ammo is powerful enough for hunting big game much past slingshot range. Still, subsonic ammo does fill an important niche for many hunters and shooters.
Lower the Boom
At sea level, the speed of sound is roughly 1127 feet per second. When a moving object, such as a bullet, breaks that threshold, there is an audible shock wave that sounds like the crack of a bullwhip. Most of the noise inherent with shooting a rifle, however, comes not from the bullet breaking the sound barrier, but from expanding gases rapidly escaping the rifle’s bore. It’s the latter bang that causes hearing damage, reveals shooters’ positions, scares game, and works Mrs. Walney down the road into a fit of agita. So while subsonic ammo does eliminate the downrange crack, and does reduce the bang at the muzzle somewhat due to its lower velocity, it won’t make your centerfire rifle sound like mouse feet on felt. It’s just one way to mitigate the noise.
Another way is to buy a suppressor (legal in 39 states), which will greatly muffle those escaping gases. Quietest of all is to use a suppressor in tandem with subsonic ammunition, which can reduce the sound of gunfire to a whimper in the rain. But there’s still the question of performance, which is significantly hampered by going subsonic.
Since energy is the product of mass times velocity squared, a slower bullet has exponentially less energy than a faster one of the same weight. Take your average 55-grain .223 Rem. bullet. Traveling at 3250 feet per second out of the muzzle, it produces 1,280 foot-pounds of energy. But if you reduce the velocity to a subsonic 1100 fps, it produces only 150 foot-pounds. In other words, it turns a .223 Rem. into a .22 LR—the difference between a load for deer and a load for prairie dogs. This is one reason why you rarely see subsonic .223 loads on shelves. The other is because a lack of energy going forward equals a lack of energy going backward—and so they can fail to cycle semiautomatic rifle actions.
To compensate for less velocity, you need more mass. That’s why rounds with long, large-diameter bullets like the .300 AAC Blackout (which function well in modern sporting arms with a simple upper receiver swap) have become the preferred subsonic centerfire round for sportsmen, as well as for the military and law enforcement. (Note that these long bullets are most accurate when fired from barrels with fast 1:7 twist rates to stabilize them.
Hornady’s 300 BLK subsonic 208-grain A-Max load, for example, delivers 480 foot-pounds of energy from a carbine’s muzzle. Think .45 ACP. But because of this long bullet’s incredible ballistic coefficient of .648, at 500 yards it surpasses the energy of a full-power 55-grain .223 Rem., and nearly triples that of the .45 ACP, and it does so in a hushed tone. That’s marginal performance for deer and hogs beyond 50 yards, but it’ll do the job on longer-range varmints where noise is an issue. This type of load is ideal for home defense, where shots are measured in feet and taken in tight confines that exacerbate hearing danger. At the very least, this ammo is a hoot to shoot on the range thanks to its mild recoil and low noise. It’s like shooting a rimfire, but with more punch.
Speaking of which, rimfires are where subsonics really shine. A standard .22 LR load delivers around 1200 fps and 140 foot-pounds of energy at the muzzle. The typical subsonic .22 LR load offers around 1050 and 100, respectively, a negligible difference to any squirrel. So while the energy to cleanly kill small game remains, the downrange crack vanishes. And as smallbore competitors know, subsonic .22 LRs are more accurate than supersonic .22s because they exhibit 37 percent less wind deflection due to the disproportional increase of air resistance near the sound barrier. When subsonic .22 LR ammo and a suppressor are combined, you’ve got a whisper-quiet, deadly accurate small-game firearm.
All the major ammunition manufacturers offer subsonic .22 LR loads. CCI’s Subsonic HP, for example, reduces velocity to 1050 fps and therefore lowers the decibel level to around 68, almost half the normal high-velocity .22 LR load. (Any .22 Short cartridge will accomplish the same thing, if your gun will shoot them.) However, subsonic rounds may have trouble cycling the actions of semi-automatics reliably. If you shoot a single-shot, pump, or bolt-action rifle, you’re good to go. If you shoot a semiauto, try Winchester’s new M-22 Subsonic .22 LR, which fires a 45-grain bullet at 1090 fps and is designed specifically to work with semis. In any case, with subsonic ammo, your rimfire will still be hard on game but easier on the ears.