A subsonic 220 grain, like a 45 ACP?
No, its .300 AAC BLK (7.62x35mm), a cartridge designed by AAC specifially to be suppressed. Its been around for a little while now and is really starting to gain popularity as more manufacturers jump on board with it. Its a great round, out of a 9" barrel using its supersonic loading it produces nearly 40% more energy than a 16" barreled 5.56mm rifle. It also uses standard AR mags and can use the mag to its full capacity, ie 30 rounds.
Here it is being fired into ballistic gel
How it sounds suppressed
Some of the companies that have already gotten behind the .300 AAC BLK
AAC - uppers, rifles, silencers, and ammunition.
Adams Arms - rifles and uppers.
AR-Stoner - barrels.
Atlanta Arms - ammo.
Barnes Bullets - bullets.
Black Hole Weaponry - barrels.
Brad's Warehouse - converted brass.
Bushmaster Firearms - uppers and rifles.
BWE Firearms - rifles, uppers, and suppressors.
CMMG - barrels, uppers, and ammo.
Compass Lake Engineering - AR barrels.
Cor-Bon - ammo
Delta Company Arms - rifles, barrels, uppers.
Dillon Precision - reloading conversion kits.
Double Tap - ammo.
DPMS - rifles and uppers.
DS Arms - rifles and uppers.
Forster - reloading dies.
Gunn - ammo.
Hornady - ammo, dies.
L ee - reloading dies.
L.E. Wilson - case gauges.
Lewis Machine and Tool - barrels, uppers, rifles.
Loki Weapon Systems - uppers/rifles.
Lone Star Armory - 300 AAC BLACKOUT marked lowers.
Lothar Walther - barrels.
LWRCI - rifles.
Match Grade Machine - Thompson barrels.
McGowen Barrel - Savage and other barrels.
Model 1 Sales - AR barrels/uppers
Montana Rifleman - barrels.
North Eastern Arms - barrels, uppers, rifles and silencers.
Noveske - rifles and uppers.
One Shot - ammo.
Pac-Nor - barrels.
Pacific Tool and Gauge - reamers and gauges.
PNW Arms - ammo.
Primary Weapons Systems - rifles and uppers.
Raven Armament Company - ammo and uppers.
Redding - dies.
Remington - ammunition.
Robarms - XCR Micro rifle.
RUAG - ammo.
Satern Custom Machining, Inc. - barrels.
Selph Arms LLC - barrels, uppers, re-chambering, and rifles.
SI Defense - barrels.
Sierra - bullets.
SilencerCo - silencers.
Southern Ballistic Research - ammo.
Southwest Ammunition, LLC - ammo.
Spike's Tactical - uppers and rifles.
Summit - ammo.
Surefire - 300 BLK sound suppressor.
The Bullet Works - bullets and ammunition.
Triton Arms - AR barrels.
Umlaut Industries - 300 BLK caliber marked Rifles, Upper and Lowers. 16" and 10" Factory Title II.
White Oak Precision - AR barrels.
Wilson Combat - rifles, hunting and self defense ammunition.