Re: BBL Life
Will it be shot hot?
What powder do you plan to use?
How often will you clean it?
How will you clean it?
Are you opposed to break in fire-lapping kits?
Can you afford the downtime of rechambering to get into new throat material?
All of these factor into barrel life.
The fact is that the 30-378 is WAY overbore and I am not surprised when I read faster velos on my Oehler when chronoing 300 ultras. The 30-378 is just trying to push too much powder down that 30 cal hole.
If it was my barrel and I were treating it the way I do, and I was expecting accuracy like I do, and was using it for ultra long range shooting the way I do, I would expect no more than 600 rounds of peak accuracy before resorting to other tricks in the bag for "reviving the beast".
Ultimately, the barrel WILL get to the point where it will not shoot the way it used to and at that point you can use a throat maintenance system from David Tubb to smooth out the barrel, and you may have to switch to a different bullet with a more gentle shape and/or move the bullet out to a longer seating depth. Or, you can set your barrel back a thread or two and have it rechambered. I have had to do this reviving many times on my own rifles. One in particular was my 300 win mag. After about 1100 rounds, my accuracy went from 1/4" to 1 1/4". I then went to a longer bearing surface bullet, moved it out closer to the riflings, and worked up the new load accordingly. Accuracy came back and has stayed for awhile, but I know ultimately some day it will need a new barrel. Oh, by the way, I shoot 75.5 grains of Rl22 with a 180 grain Accubond and have 1300 rounds through her now. The 30-378 burns about 20-30 grains more powder so expect at least 30% less throat life.
If it's not far, it's boring.