Rimfire5, some comments for you. . . .
Sierra Bullets' never made any ammo; just bullets.
Barrels chambered for the .308 Win. typically last 3000 rounds for best accuracy from match grade barrels. 5000 to 6000 in factory sporter barrels. After those numbers, their owners typically start seeing accuracy degrade to the unsatisfactory level.
If one cannot get best accuracy with the .308 case by properly full length sizing it, they're not doing something the best way. It'll take a very close look at the details to find out what the problem is. The round count in your barrel's near the top of my list of probable causes. Another is what method you use to measure accuracy; group averages ain't all that great. Would have been better to shoot all those groups with a given load on the same target; instead of 5-shot groups fired 4 times, shoot one 20-shot group.
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master