I no longer load anything below about 7500 psi, 12 gauge or otherwise.
I keep the load reasonable as in 1 oz-1 1/8oz @ no more than 1200 fps, usually a bit lower, in 12 for protection of the wood, etc. If a gun is not capable of handling this pressure it's a "WALL HANGER".
With this in mind, I use the fastest powder that will give the desired load within that pressure. This keeps the peak pressure as close as possible to the breech with a rapid fall off as it goes to thinner sections of the barrel.
This has worked well for me over the years for any gun built after smokeless was regularly used. In the case of an earlier gun, say pre 1890 with very light breeches then I only shoot "Black".
