I have lots of 308s and never got a 1" group, but I did quick and dirty rebarreling on some surplus Mausers and converted them to 308 and took them to the range Jan 29, 2009.
That day I had (4) different 308s shoot a 1" group at 100 yards.
The load was 110 gr Vmax ~ 3000 fps.
This is a wimp load, but it gets the job done.
All those years of shooting 168 gr Match Kings never got me a 1" group.