If the round is loaded to maximum or +P pressures, then age will not be nice to the next user. Heat ages gunpowder, in fact, it is an exponential function, the hotter it is, the faster gunpowder deteriorates. Heat is used by the Military to artificially age gunpowder, primarily to determine the shelf life left in the lot being tested. The rule of thumb is if the powder fumes red within 30 days, while being baked at 165 F, then it is too unstable to keep in inventory. Also, as gunpowder ages, combustion pressures go up. This is an example
So, lets say the SLAP round was a maximum round when it was new. And then at some point in its lifecycle, some ammunition specialist tested the powder in that lot and found it was giving excessive pressure, or, (worse) reports from the field indicated blown or damaged 50 calibers, then that lot was pulled, and scrapped. And then some of that lot, instead of being milled, as it should, worked its way through the aftermarket chain, and ended up in Kentucky Ballistic's rifle. And blew it all to hell. That is one story.
I will say, denialism about gunpowder aging, and the bad things with old gunpowder, is strong, pathological. There are posts in this forum where gunpowder deniers use all the typical arguments that deniers use: "Prove this, prove that, yes ilitary gunpowder ages, but not gunpowder in the real world, and prove someone has been hurt, or prove that millions or billions have been hurt, etc, etc."
