Just bought a 300NM today. So I have spent the day learning so much from everyone who has contributed to this thread, thank you!
This has been a great help learning what loads to work up.
In putting an order together with one of my wholesalers I found this statement regarding Peterson brass in the 300NM.
NOTICE - THIS IS THE FIRST RUN: Due to popular demand, Peterson Cartridge released its .300 Norma Magnum and .338 Norma Magnum casings in the spring of 2018. When Peterson designed these casings, it chose to use the same parent casing as its .338 Lapua Magnum casing. As a result, Peterson chose to keep the major diameter of the casing (the diameter just above the extraction groove) the same size as its .338 Lapua Magnum casings. That diameter is .580”. Since Peterson has never had any complaints about excessive major diameter growth, or primer pocket loosening in its .338 Lapua Magnum casings, they believed that to be a fine decision.
After releasing its 1st production run of .300 and .338 Norma Magnum casings with a major diameter of .580”, it was brought to Peterson’s attention that some customers would rather the major diameter of the Peterson .300 and .338 Norma Magnum casings be the same size as the .300 and .338 Norma Magnum casings produced by Norma. That diameter is .583”.
Peterson has received a lot of compliments on its first run of .300 and .338 Norma Magnum brass. Customers have stated that the Peterson casings hold more pressure, and that they can get more reloads. Several have said things, like this customer who enthused, “The Peterson Brass I’ve been testing in .300 Norma Mag is by far the best .300 Norma Mag brass I’ve used to date. The accuracy is outstanding.”
After studying the potential problems associated with changing its .300 and .338 Norma Magnum major diameter, Peterson decided to modify its tooling to change the major diameter of its .300 and .338 Norma Magnum casings to match Norma’s major diameter which is .583”. As a result, all future production runs of Peterson’s .300 and .338 Norma Magnum casings will have a major diameter of .583” to match the Norma Magnum casings produced by Norma.
Steve