I have found lower SD's with 450's than the 400's. If you are shooting a larger capacity (over 35 grains of powder) SRP case, the 450's are definitely a better option. I use 450 primers for my 6 CM and 308 with Lapua SRP cases. My smaller 6BR variant cases all get BR4's.I have seen it written that 450 primers are slightly hotter, thicker and have less fliers?
I have only used 400's.
Any truth to those claims?
Cheers