Dear Sir,
I just got home from the shop, that is where the 300 ultra brass is. If I remember correctly, the comic books stated that the UM case has 13% more capacity over the 300 WBY. Based on that I ran with a case overflow of 113 gr of water. If it is much different than this, post the volume/weight.
90 gr RL 25, 220 MK 3.65" oal, 26"bbl, Case volume of 113 gr. water. 2925fps/58500psi.
I have found that using 58000 as my max number corresponds well to what I have read on my brass. Asking for a 65000psi load results in primers you can remove with a good puff. I have found that QuickLOAD is right on the money with Hodgdon powders, but it out with RL-XX. Use caution, start at about 80 gr of RL 25, please don't sue me....