all of my test stuff for the LR308 has been on a 16" carbine gas upper that happens to like 168gr amax. Have gotten similar results with both varget and H4895, multiple loads that produce sub 3/4" groups at 100 yds. Likewise for the 165gr SST.
working on putting togther a rifle length gassed upper - 20" mega barrel. Hopeing it'll help me fine tune and work out the lock-time bugs i was fighting with the carbine gassed upper.
tell us a little more about your son's gun and i'm sure you'll get lots of information back - barrel length, etc 
