Re: Effects of long seating on pressure?
To answer a couple of your other questions. All barrels shoot differently, just because a test barrel did X doesn't mean yours will. I've got two 6.5X47 Lapuas. Both chambers mad with the same reamer. Both 28 inches, Identical rounds shoot 60fps slower in one, with higher pressure. I can't reach the MV of the other gun and stay within safe pressures. The books MV are for reference only. Your gun will shoot what your gun shoots. Starting with a hot load can get you killed. Start moderate and work up.
Allways shoot two or more foulers before you shoot for group. 3 round groups are 69% as big as 5 shots groups. But usually tell you what you need to Know. Always hunt with a fouled barrel, and always make sure your first shot, is what your scope is sighted for. A hot barrel may move the POI and when you are hunting, only the first, cold bore shot counts.
The serious BR guys shoot 10 shot groups. But they wear a lot of barrels out... A gun that shoots MOA with 3 shots, won't shoot MOA with 5, and MOA gun with 5 shots, won't be MOA with 10. To shoot real, live, no kidding around "what is can me and my rifle really do", you've got to shoot 10 shoot groups.
But remember, when you hunt, your first, cold bore shot is the only one that counts.