You've asked a question that can' t be answered without knowing your guns internal configuration, particularly the throat if a revolver, the bullet type, and perhaps most important of all the lubricant being used.
As the alloy is softened with most bullet lubes on the market, pressures climb dramatically, while with LBT lubricants, pressures go up so little that it is normally of no concern with alloys down to as soft as 8 - 10 bhn, which is freshly cast air cool wheel weight metal, this if the load is listed as generating pressures under 40,000 psi.
The main function or purpose of having bullets real hard for revolvers is to prevent them from swelling out into the huge throats of todays revolvers, where they will have to be sized back down to barrel diameter, and that against a relitively rough surface. A load listed at 40,000 psi with hard bullets, when lubed with most commercial bullet lubricants can generate enough force against the forcing cone, and increased pressure with the slower burning powders, to actually crack the barrel at this point. Understand that with most normal loads in revolvers, maximum chamber pressure occurs long before the bullet base leaves the cylinder, in which case it probably will not jump up to danger levels if the bullet wedges in the force cone as described above. If bullets are soft enough to swell out into the forcing cone, accuracy will be degraded by the deformation of swelling and sizing back down, in many revolvers a good one thirtysecond of an inch. This accuracy deterioration is the main reason to use hard alloys, not pressure concerns. In other words, use the alloy hardness that produces the best accuracy in your gun with the load you want to shoot. Even air cooled wheel weights which have been aged a couple weeks, and produce a hardness of 12 bhn, are too hard to mushroom on game, though they will batter a bit if they hit large bones, but not enough to hurt killing power in most cases.
