Re: 240 weatherby mag
Barrel life is certainly hard to predict in any configuration, not to mention a hot 6mm. Your barrel will last longer, read less throat erosion over time, if you are not shooting 10 shot strings in competition. If you are using this rifle as a varmint rifle or hunting rifle, then you will most likely see many years of service before you have any discernible throat erosion. If I had to take a guess at round count, I would say acceptable accuracy would last for approximately 600-800 rounds.
My rifle was built as a dedicated groundhog rifle, with no concern about barrel life. I figured I would get many years of use before I had to re-barrel. Six years later, it's still shooting well.
My velocity is accurate as I have clocked it over an Oehler 35, 43, and PVM22. I'm running a Hart 28" barrel that may be on the fast side.
When I built the stock, I conducted a brief round of load development to verify my load. It grouped in the .1s at 100, and hung around 1" at 300 yards.
If you're concerned about blow ups, you may consider using a 9 twist. The 9 twist will stabilize the 105-107 bullets easily. I have shot the 105 A-Max, 105 Berger, and the 107 Sierra in my rifle. The barrel likes them all equally as well, I just chose the thinner jacket bullet for the dramatic effect on groundhogs.