When I first start loading with a 300 wby I load 82 grains of H4831, cci250 primer and seat the 180 just short enough so it will feed through the mk 5 action. This is a generic accuracy load good in any 300 wby with freebore. I always try this first to see if it is a shooter. I have never seen a mk 5 that did not shoot this load well. Velocity is right at 3200 fps in a 26" barrel. Some newer powders will get more velocity. But this is a shooter to try in any 300 wby.
27-inch barrel 3-groove. I get 2975fps average with 80.5grains of H1000. Fed215 primers. It will go faster, but this load has the best extreme spread. FWIW.
Here are some related products that LRH members are talking about.
Clicking on a product will take you to LRH’s partner,
Primary,
where you can find links to LRH discussions about these products.