Re: 30-378 200 grn Accubond Load
My Accumark barrel loved 106.5 Retumbo, FedGM215 primers, under the 200 Accubonds. A load I used to get several long range woodchucks, including one at 1198, and a 660 deer with a few years back.
I also see in my load notes "109 TOO HOT".
I would do a ladder from 104 to 108.5 in half grain increments to see if anything stands out.
Also here is a little test I did with my last 30-378 barrel, just prior to swapping it that I thought might be useful.
While I usually don't beat on skinny barrels too bad, I had already made up my mind I was going to replace it with a heavy custom. I also intended to have the action trued up, which meant that I wouldn't be able to use the barrel afterward.
The "testing" so to speak started with the Retumbo load listed above. In one sitting I sat and threw 40-50 of them, learning wind, I paused for different changes I noted with the wind and what it affected, etc. Shots were probably less than a minute apart. It took quite awhile scrubbing but it recovered.
Then I tried the H50BMG load on a different outing. That test consisted of 25 back to back and got it hot. Again some pretty good scrubbing and all was well.
Third time I had a decent load with RL25 and 220mk, second and third rounds busted clay birds (after an angle and wind correction found with the first) at 1K. So some friends and I went for gongs, clays etc. Somewhere shortly after round 20 things went bad in a hurry and 1/2moa went to BIG. No amount of cleaning helped it, and I was aggressive in my attempts to get it clean. There were a couple of major lumps I could feel and never get out of the barrel. Test was done, new barrel went on.
I have since avoided RL25 in this caliber, but continue to use it for a friends 300 rum I load for, which sees very little use(abuse).