Re: Why start at 10% below maximum?
That (safety) is what raises my curiosity. I can understand that accuracy could be down in the lower ranges. However for hunting, if the accuracy has to sacrifice more than 100 fps below a reasonable max load, then I would look for a better suited powder. Hunting bullets are Nosler Partitions (non-negotiable)
So, that brings me back to the original question. I fail to see where it is any safer buying a factory load that is going to develop a pressure comparable to the maximum load in the loading manual than it would be starting a loading process at something greater than 10% below the load in the manual that is equivalent to the factory load. If that is really a legitimate concern, then I should be buying reduced factory loads to be sure they would be safe in my weapon.
I can readily see where it would be necessary to back off the maximum because of some variation in primer/powder relationships (and others). But the 10% to me is excessive. 5% is more realistic for safety reasons.
But no one has actually answered the other question. Has anyone experienced any loads that were "normal" (not shoved into the lands, etc. and loaded according to the manual and good practice) that were less than 98% of maximum recommended that exhibited excessive pressures? I never have. In fact, I have rarely seen one at maximum load that exhibited signs of excessive pressure.