Before going farther, I needed to know what the throat of my rifle's chamber looks like. I have a Hornady OAL measuring gauge, and ordered a .264WM modified case. With it I measured the base to lands distance: 2.762". Wowza - that's WAY short. my 7mm mag is 2.759" (basically the same) and it's OAL is supposed to be 3.29", not 3.34" like the .264WM. In orther words, the .264WM's throat is ballpark 50 thousandths short for the SAAMI OAL. The tech note was right.
This is important information, as blindly loading to SAAMI spec could create a bomb. It also explains what's wrong with the Hodgdon data. They're loading to 10 thousands OVER SAAMI length with a round nose bullet. If their chamber looks like mine they're easily 60 thousandths into the lands - probably more. I don't know what the nose length on that Hornady round nose bullet is, but it has to be short. When you jam the lands, you have to drop the powder charge to keep pressure in line, and you net lose velocity. Sure enough, the Hodgdon data is low on charge weight, high pressure, and slow. Now I don't know what barrel they used to test, and I'm sure it's not a factory Winchester because their data says 1:8" twist, and Winchesters are 1:9". But whatever it was, they must have reamed it with a reamer a lot like the Winchester reamer.
QL can be set to model bullets jammed into the lands by increasing the shot start pressure. When I do that, it says the max load for Retumbo would be 65.6gr (vs. 64gr book load) and that with the 64gr load velocity would be 2864 ft/s vs. 2846 ft/s book. Now everything matches and the world is as it should be. With everything matching up, I feel good about using QL to create load data.
Now to re-configure QL for what my real load is going to look like: the Weldcore instead of the Hornady, OAL of about 3.29" (NOT 3.34") and since I'll now be back off the lands, a normal shot start pressure. Plus my barrel's a 24", not a 26". With all these changes here's the powder list I get:
Of the top powders, Retumbo and Norma 217 are in the garage. I'd rather use Retumbo, so that's where I'm going to start. Nominal max velocity is 2930. I'm going to use a Lee Factory Crimp die (these are hunting loads I want to be tough and waterproof), which changes charge weights and pressures a bit but the basic approach will be to use a chrono and load to velocity - whatever charge of Retumbo gives me 2930ft/s is max. Because of the crimp die I expect to get there a couple grains below 68.7gr. I'll start nice and low and watch both velocity and bolt lift. Due to not jamming the lands, my charges are heavier and my velocites higher than what Hornady got without exceeding SAAMI max pressure.