These two cartridges use improved 300Wby cases. They should provide 100 to 200fps more vel for equivalent bullet weights. You can start with mid range loads from the 300Wby and work up. Depending on the throat, these loads should be safe as a starting point.
Neck size so the case headspaces on the shoulder and enjoy...
On the 308 Baer, if you use 300 wtby brass, you will end up with short necks. Most use 375 or 340 wthby and neck down to retain long necks.
Call Bruce Baer at (717) 349-4077 or [email protected] and get the info straight from the horses mouth. He already has die sets made up, so I would have him do my chamber as it saves $ on ordering a chamber and sizing reamer and you know that they all work.
I am not sure about the shoulder angle. Contact Mr. Baer for that info.
There is some "research" going on regarding shoulder angles and neck lengths with respect to throat erosion. Most of this work is being done with 6mm wildcats.
It seems that the longer the neck, the higher the percentage of powder ignited in the case. This apparently leads to less throat erosion. Similar case capacities were compared with the same bullet in these tests (see Articles in Precision SHooter this year).
Shoulder angles didn't seem to do much. Most will be 30 to 40 deg because it handles case stretching better.
The RUM should wear the throat faster simply because more powder is being burnt with each shot. The improved WBY are using around 85 to 90gr and the RUM 100gr+.
For BR shooting, you want to use the smallest case you can to launch the desired bullet. Easier to tune and less muzzle turbulence.