Let me start this off by saying this is my first post here, so I'm glad to have finally made it out of the shadows. Lots of good information on this forum. I've got about a year of reloading experience, 6.5 Grendel, 9mm, 10mm, and now the 450 BM. I use the 10th edition Hornady book which has been fairly close to most of the charge weights and corresponding velocities.
That is until I loaded my first 450BM loads today. I'm using 250 grain XTPs, 300 grain XTP mags, new starline brass, CCI 41 primers, seating to the cannelure, and taper crimping to .476. They are fired from my 18" AR15.
I started the 250s at 37, 37.5, and the book max of 37.9. I realize these numbers are for the non cannelure 250 FTX, but they are more conservative than the 240 xtp mag. Groups shrank from about 4 inches to 2 inches and the SD dropped as well at max load, but my average velocity at 37.9 was just so of 2400 fps. That's a full 200 fps faster than the book. From what I can tell the fired brass looks (measures) similar to Hornady black.
Similar story with the XTP mags, with about 2000 fps velocity (100 fps over the book) and about 7 inches lower impact from the 250s.
Sorry for the long winded rant, I just want to make sure everything is safe. The book published max load had the best standard deviation and 3 shot group so I'd love to use that load if I'm not prematurely wearing out my brass/rifle.
Thanks!