OzFclass

g'day all once again.

today i have a question about case trimming. as ive ordered my case trimmer, i thought id look up the spec for my case length,
according to the lyman book, my 300RUM case should be 2.850 inches long, which is fine, until i measured my cases expecting over this, and found my twice fired cases are still shorter.
is the lyman book wrong or is there something going on with my cases?

happy shooting!

Nothing wrong and this is common. Shells have to be less than the recommended length and sometimes quite significantly. Set the trimmer up 10 thou under SAAMI max and you should be safe.

Alternatively it is worth checking your actual chamber length if you get the chance. Sacrifice one shell and cut half the neck off leaving you a collar and much shortened case. Debur collar and shell and seat a projectile in shell. Slip collar over top of projectile and close the bolt. This will give you your actual chamber length and you should trim about 10 thou short of that.

Check your brass length before and after fire forming on the first shot.
Don't be surprised in they actually get shorter as they form to your chamber.

cheers for the info guys

now i just have to wait for my trimmer to turn up, hurry up postie!!

happy shooting!