I've located a 10" 454 barrel which I've considered having rechambered for the 460 S&W.
I've wondered if the twist rate would be correct for the 460 with it's faster MV, but I guess your's is accurate so that may answer that.
What kinda groups are you getting from yours and at what distance?
I think the gain twist is more for them 2300 fps 200 gr bullets. I am not pushing them quit that fast using the 240, 260 and 300 gr. bullets.
My groups are 2 inches at 100 yards. I was not using the best rest and did some quick shooting because it was a little cold out.
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I think when it worms up some I will be able to get out and do more shooting. The muzzle break sure tames the recoil. When I shot the 454 Casull barrel with hot loaded 454 Casull rounds it was a handful, now shooting the 460 Mags with the muzzle brake, it has less recoil that the 454 Casull rounds without the muzzle brake.