[LouBoyd]

My gunsmith has suggested that he can make a 338/7mmBR chamber by first running a 7mm BR reamer with a 338 pilot, then run in a reamer for a 338-06 to cut the neck them a 338 throat reamer if the throat needs to be deeper (it will for 300 SMKs) Personally don't want a 338/7BR in an AR-15 becasue the magazine won't handle the long bullets and if it won't magazine feed why bother with an AR? It would work in an AR-10 or DPMS LR-308 which already has the right bolt face. If the magzine is too short to load over 240 grain 338 bullets you might as well use the 300-221. With subsonics about all you get with larger diameter bullets of equal weight is lower BC and less range,

Max weitght for available bullets
224 - 90 gn Matchking
264 - 142 gn Matchking
284 - 180 gn Berger VLD
308 - 240 gn Matchking
338 - 300 gn Matchking
375 - 330 gn Lehigh (solid VLD) 350 Wooleigh not VLD
408 - 375 gn Lehigh (solid VLD)
416 - 582 gn Lehigh (solid VLD) 700 gn cast bullets not VLD
500 - 600 gn SPRBT (for 50 Beowulf or 500 S&W stanadard chambers) Not low drag.
510 - 800 gn Barnes solids

If you know of heavier commercially avaialable low drag bullets in each caliber I'd be interested.