The .223 is a pretty powerful round and that would count (IMHO) as a high powered rifle round. And, yes, it's probably an AR-15 variant given that the Waco police were seen on camera at the site of the shooting using these pricey rifles to break open windows.
The .223 is a pretty powerful round and that would count (IMHO) as a high powered rifle round. It really isn't, 1300 ft/lbs at muzzle twice as much as a .357. 7.62x39- 1537, 7.62x51 (.308) - 2802. For comparison 30.30 - 1600-1900 depending on load.