allaroundhunter, it wasn't the benchresters shooting .308's that had to use 30" barrels; they used 20 to 22 inch ones for benchrest some years ago.
It was the Palma rifles used in prone matches at 800 to 1000 yards with 147 grain arsenal bullets from 7.62 NATO ammo in 30" barrels (the Brits were the first to do so). Was the only way arsenal ammo could shoot those light weight bullets fast enough (3000 fps or so) to keep 'em supersonic to 1000 yards.
Jimro, when Sierra's 155 gr. 30 caliber bullets were first used in competition, some folks' 26 inch barrels would not shoot them fast enough to stay supersonic at 1000 yards; even at 6600 ft. altitude. In my own tests with two .308 Win. barrels with .3075"/.2980" groove/bore, diameters, the 32" one shot the same load out at a bit over 3100 fps; about 200 fps faster than the 26" one. 30" barrels are pretty much the world standard for Palma rifles using 147 to 155-gr. bullets in a .308 Win. case. A 25 to 30 fps change in velocity for each inch of barrel length's about normal for the .308.
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
Last edited by Bart B.; February 24, 2013 at 11:12 AM.