Smith & Wesson is adding the .300 Whisper chambering to its M&P15 lineup. It's the first production AR-15 to chamber the cartridge. It has a 16-inch Melonite finished chrome-moly barrel with 1:7.5 twist and 5R rifling (the latter a contribution from the designers at Thompson/Center, who have been using 5R for years; T/C is owned by S&W). The twist rate is designed to accommodate the very light/very heavy bullets employed in the .300 Whisper — more on that in a minute — and the barrel is threaded 5/8-24 for a suppressor and comes with an A2-style flash hider. The gas key and bolt carrier are chrome-lined.
The upper and lower receivers are forged 7075 aluminum and coated with Realtree APG finish. It's optics ready, courtesy of a Picatinny-style rail on the upper. The rifle sports a single-stage trigger, integral one-piece trigger guard, dust cover, forward assist and six-position collapsible CAR stock. It ships with a 10-round magazine.
The M&P15 300 Whisper will also be available with a black tactical upper featuring a 10-inch free-float quad rail and a Yankee Hill Phantom flash hider. The upper is compatible with any mil-spec AR lower.
If you're not familiar with the .300 Whisper, the cartridge was designed by JD Jones of SSK Industriesand is currently a
factory round from Hornady. It's based on the .221 Remington case necked up to .308. The round was designed to meet two criteria: be compatible with the AR-15 platform, Contenders and bolt-action rifles; and be easily suppressed.
The low-recoiling .300 Whisper comes in two flavors: subsonic, heavy-for-caliber bullets; and moderate velocity with light-for-caliber bullets. Hornady's loads include a 208-grain A-Max at 1,020 fps muzzle velocity, with a muzzle energy of 480 ft.-lbs., out of a 16-inch test barrel. At 100 yards it's doing 993 fps and 455 ft.-lbs. and at 200 it's generating 968 fps and 433 ft.-lbs.
Hornady's light-for-caliber offering is a 110-grain V-Max that produces 2,375 fps at the muzzle for 1,377 ft.-lbs. of energy (16-inch test barrel). At 100 yards it's going 2,094 fps (1,071 ft.-lbs.), and it's still running 1,833 fps for 820 ft.-lbs. at 200.