Not familiar with RL 15 in 308, so looked at some manuals. Pretty wide variation in what they consider max charges.
When loading close to max, especially in rifle, prefer to be using a chronograph. This at least allows you to see if your loads are getting close to the velocity's from the manuals. Course taking into consideration length of barrel they used and other variables.
If your velocity's re higher than those they list, likely your pressures may be also. When I see this in loading, am inclined to back down a bit. And have seen velocity's decrease with increasing powder charges, but not very often.
Have no clue what causes it, but it does make me more careful.
When loading close to max, especially in rifle, prefer to be using a chronograph. This at least allows you to see if your loads are getting close to the velocity's from the manuals. Course taking into consideration length of barrel they used and other variables.
If your velocity's re higher than those they list, likely your pressures may be also. When I see this in loading, am inclined to back down a bit. And have seen velocity's decrease with increasing powder charges, but not very often.
Have no clue what causes it, but it does make me more careful.