300 win mag initial loading of new brass.

[kfd518]

I am getting ready to load for a new 300 win mag with .021 space between shoulder or cartridge and chamber shoulder. I have made a false neck in 20 cases, 5 of which I loaded some 125 gr projectiles in with a minimum load and confirmed the .021” space.
This difference is only measuring to be 0.5 grains water MAX with an average of 0.3 grains water.

I would like to start load work up but I am debating if
1.) I should load a bunch more with the light projectile and fire form them before doing load work up?
or
2.) proceed with load work up with cases that only have a false shoulder formed and fire form them as I use the loaded ammo and re-work the load after this batch of brass is all fire formed?

 

[AJC1]

I would fire form fun shooting before serious load development. Peterson makes longer 300mag brass with longer shoulders.

 

[kfd518]

Have looked for “Peterson long” in stock for 9 months. Time to start working with what I’ve got.
Other thought I had is load of the light projectiles I have as range ammo and as I get them out of that process use them for long term Load development.
Wasn’t sure what people’s thought on doing this the same but loading hunting ammo with 165 TTSX them moving that brass up to heavier Bullet weights after it is formed.