I would drop back to your 77.5 grain load if that was performing well. Your chronograph is telling you somewhere around 78 grains is max./near max. for your rifle. The slight increase in velocity is not worth it. The velocity you are getting now may indicate you are already over SAAMI pressures which is 64,000 psi. I have run the WSMs up to what should be 65,000 psi and things got squirrely. Even a fouled barrel could run up pressure too high.
As far as seating long it can take up to two grains more just to reach the velocity I get in a standard chamber. But I don't expect to get a significant increase in velocity by seating long. It's about like the difference between thick and thin brass. Loads may be one or two grains different but the velocity will be about the same +/- 50 fps. at the same pressures.
I revert to the bad old days of P O Ackley, Bob Hagel et all and will run up to an overload just to see how much powder that is, this is pretty unscientific as it is based off the usual voodoo signs but it alleviates the concern that my loads are over the limit but not showing pressure signs. I don't load till I blow primes like the old timers did. In fifty years of reloading I have never blown a primer. I have come close but never had anything more than severe cratering or a stuck case.
Last edited by Tejano; 07/19/19.
