I have a friend that is looking for a used AR style rifle chambered in .243, if you have one to sell let me know.
Do you have a link for the oly in 22-250? I don't see it on the web site.Olympic Arms is selling a .22-250 AR15 that was redesigned in the magwell and with proprietary magazines to allow for the longer bullets.
Saves a lot of weight over an AR10 model when your'e actually fielding it.
Also, 6.8 when translated is .277 caliber. It uses 30 caliber brass, but necked down to .277. Although not a true .270, does well on medium game.
I understand that you were looking for a 243, but these are close as I know of in the AR15 platform.
As others have said, you'd need to look into the AR10 for that, but hope some of this may help your friend.