RJ are you confusing a chamber dimension measurement with a SAAMI standard cartridge measurement? For example you measure 3.088 total overall cartridge length base to tip using the Sinclair tool. This was to find the total length of an assembled cartridge/bullet combo that would touch the lands in your chamber. The reload manual, Lee 2nd edition list SAAMI length @2.810. That 2.810 is so any and all .308 factory ammo @ 2.810" will fit in any .308 auto, lever or bolt gun.


You however are looking to load a cartridge to the length that custom fits your chamber as far as length. So think about this. Any factory .308 cartridge you can buy will not exceed the SAAMI length of 2.810" and will physically fit in your chamber. However you wish to custom assemble a cartridge that will be a custom length based on your chamber and your freebore and the lands as a reference.


I would think about loading to your chamber dimensions and at the jam or jump you wanted, with the obvious thought of possible pressure issues(being near the lands) and magazine interference length.
Hope this helps.