How Do I Arrive At An OAL?

[SporterII]

Clean Slate.
280 Remington brass. 162 Amax and 168 Sierra 7mm bullets. Plenty of room to feed from my BDL mag box which is how I would like to run it.
I assembled a dummy with the bullet, where the boat tail blends into the major diameter, just above the base of the neck.
You place it from there, please.

 

[flashhole]

For that cartridge case a 168 grain bullet is considered a heavy bullet. I shoot 175 grain bullets in my 7mm Rem Mag which has considerably more powder capacity. Nonetheless, you need to select a powder that will work well with that bullet/cartridge. I suggest Hodgdon Retumbo.

The first thing you need to do is a Optimum Charge Weight (OCW) test using different powder charges (by weight, I suggest 0.3 grains difference) and determine where your accuracy nodes are from 200 - 300 yards, 300 is better. Do a Google search to study OCW, it is a great method of determining your "production" powder charge. Choose the highest velocity node and do the test again with smaller increment charge wieghts.

Next is changing the seating depth in small increments to give the best accuracy.

 

[SporterII]

My question really relates to how deep in the case these bullets need to be.
There is no chamber cut for them yet.
I know from shooting 7-08 that my OAL is way longer than sammi. My chamber is cut accordingly. My '08 bullets still have the entire neck holding bearing surface. The 280 has room for more and I do not know what the parameters are or what others arte using successfully.
My dummy round is 3.465" with most of the neck holding.