You are seating .020" off the lands, how does that compare OAL to the loading data you are comparing to? If you are seating significantly longer than the data you are trying to emulate, the pressure and velocity will be less. Have to add more powder to get the same velocity. Hope that makes sense.
I suppose this isn’t a thing I’ve really thought about. My plan was to start @ 20k off the lands with a bunch of different charge weights, find the most accurate one with along with some good velocity. Then I was gunna take that powder weight and mess with seating depths next. But you fellas are making me wonder if I’m thinking about that right.
No, you have that right. 0.020 off the lands is a great place to start. After you find a node or accuracy with your powder charge weight, then you can fine tune with seating depth if necessary. Some bullets are very finicky to seating depth and others aren’t. Just know that you may also see fluctuations with pressure and velocity, so monitor your pressure signs with any change……especially if you are playing with the upper end of safe loads.
I have never loaded 7 mag so I don’t have much to offer for powders based on your bullet weights. H1000 is a recommended powder and should do fine. Also….full length sizing is widely accepted by some of the best shooters in the world. Neck sizing, though still used, has mostly gone by the wayside. There are lots of great videos on YouTube that explain why….and Erik cortina has one of the best. You could learn a lot by watching some of his videos.