Re: .300 Jarrett compared to the .308 Baer...
From an accuracy standpoint, I found the best load for my 308 Baer this weekend. The load was RWS cases (375H&H necked down), CCI 250 primers, 180 Sierra MK & 81gns of H4381. I chose the H4831 as I thought H1000 may be a little slow, but I still plan to try H1000 over the next few weeks.
As far as I know, the 300 Jarret has a steeper (40 degree?) shoulder which is blown slightly further forward than the 308 Baer. Loads for the Jarret will be very similar to the 308 Bear, but could be just marginally hotter. I usually use 300 Wby data for starting loads if I have no other data available for a bullet weight or powder I want to try in the Baer.