I think there has been a lot written and talked about of the overall length when building a load. OAL is easy to measure and specific to one bullet and one powder (burn rate) when talking load data - the combination of powder charge and OAL.

What is really of importance is not so much where the nose of the bullet is but where the base of the bullet is within the case ("pressure chamber"). Hence, the large amount of data on OAL being specific to a particular bullet/powder combination. Now toss in the surface coating of the bullet whether it be lead, plated copper, copper jacket, HiTek, powder coat - - - and we start dealing with barrel friction effects on pressure .