300 WinMag question

Discussion in 'Reloading' started by griffin ordway, Sep 27, 2018.

  1. griffin ordway

    griffin ordway New Member

    Sep 25, 2018
    Hi All,
    Not trying to stir up old threads....I've done massive research regarding reloading the 300 winmag, on this and other forums, and I can't find the answer to some specific questions. Just for some background: I am not new to reloading, but am fairly new to the belted mags; I am loading for use in a extreme long range target rifle (AX300); I will be using 195 grain Sierra TMK's; Using Norma brass.

    1) Every reloading manual I have (quite a few!!!) shows the Max Case Length at 2.620, and the Trim To Length at 2.610...I have my trimmer set to 2.605 because there has not been one single virgin case that I've measured over 2.603! Once fired, they only expand out to about 2.608 max. Is this the norm for Norma brass, to be .007 short of Trim To right out of the box?

    2) I totally get the whole "headspace" question with belted mags....that after the first fire forming, I am looking to headspace off the shoulder. My question has to do with bumping the shoulder back. My measurements show that after the first firing the case has stretched about .018, but then after the second firing it has stretched about another .003. So, do I bump the shoulder a couple thou after every firing, or just neck size until hard to chamber and then bump the shoulder. I've read a GazziliaMillion varying opinions on this....some even claiming one should FL size the case every firing (which I know is just wrong, but still believed by some).

    Sorry for the "windiness" of my questions, but thought background and specific numbers would help.

    Thanks all!!
  2. cohunt

    cohunt Well-Known Member

    Jan 21, 2016
    Consistancy is accuracy
    Perfect practice makes perfect
    Reloading is frustrating but rewarding
    Everyone has their own reasons

    Personally, I fl size every time but bump my shoulder .0015" for bolt actions and .003 for semi auto.
    As far as trim length, I let my brass grow past the minimum trim length then keep them at minimum...others like maximum length....

    Your rifle will tell you what it likes
    rfurman24 likes this.
  3. dok7mm

    dok7mm Well-Known Member

    Apr 13, 2015
    I don't bump the shoulder after first firing. As long as fired brass will chamber, I neck size.

    On trimming, I measure chamber OAL or consult my reamer print. Also, measure your brass length AFTER FL resizing. I run .005" short of max length. That helps prevents excessive carbon build-up in chamber neck.
  4. Deviant

    Deviant Well-Known Member

    Jul 12, 2018
    I would FL size but don't bump the shoulder until after second firing. I dumped my neck sizing dies years ago and haven't looked back. Just because you FL size does not mean you have to bump the shoulder every time.

  5. Trnelson

    Trnelson Well-Known Member

    Feb 15, 2012
    I have had the best results, in my rifles, by neck sizing and only doing more than that if I had a hitch in chambering. Usually it’s after the third or fourth firing that I have a need to bump the shoulder back. If your rifle works better with a FL size, then run that!
    As far as maximum case length, I keep my cases 0.005” of case length shorter than the actual maximum length my rig can chamber safely. Just cast the chamber and it will tell you everything you need to know. I rarely have an actual need to trim before the fourth firing. I anneal after every firing though. If your rifle delivers what you are looking for by trimming to 2.605” then run that length!
    Reloading and long range shooting is a game of consistency. Record and control as much data as what you have to to get to the results you are trying to get the rifle to accomplish the results you are looking for. Some rigs are just more finicky than others and need more attention to produce adequate results.
    Lastly, and most importantly, have fun and be safe.