The 308 gauge is not the same as the 7.62x51 gauge. There is around 4 thousandths longer length to the 7.62x51 gauge. This is because military rifles have a more generous chamber to account for heat and other factors that are not generally encountered with 308 chambered rifles. 308 ammo also has a shorter OAL, which is one reason why it is not recommended to shoot it in M1A rifles.
![L1A1 🇬🇧 SLR [British FN FAL - Iron Sights] to 600yds (Feat. Bloke on the Range) Practical Accuracy](http://i.ytimg.com/vi/q0j3AAfte2w/mqdefault.jpg)
![L1A1 🇬🇧 SLR [British FN FAL - Iron Sights] to 600yds (Feat. Bloke on the Range) Practical Accuracy](/img/tr.png)
The 308 gauge is not the same as the 7.62x51 gauge. There is around 4 thousandths longer length to the 7.62x51 gauge. This is because military rifles have a more generous chamber to account for heat and other factors that are not generally encountered with 308 chambered rifles. 308 ammo also has a shorter OAL, which is one reason why it is not recommended to shoot it in M1A rifles.
So what size did you end up using on the locking shoulder?
The real tight one, .256"
Did the bolt loosen up after breaking it in?