Magnum primers for 9mm

Discussion in 'Ammunition & Reloading' started by amstutz, Jun 15, 2014.

  1. amstutz

    amstutz New Member

    I stopped in my local gun shop on sat to inquire about supplies. No powder but he had a box of primers. When he handed it to me I noticed they were magnum primers (cci 550's). I looked puzzled and he quickly said "these are fine, no problem, don't worry use 'em just like the 500's I promise you will have no problems at all". I bought them. And now am having second thoughts. I'd like some opinions from you experts. Should I use them the same as the 500's? Or not?
  2. c3shooter

    c3shooter Administrator Staff Member

    No, you don't.

    Magnum primers have a pinch of powdered aluminum, burn hotter, giving higher pressures.

    General rule of thumb is reduce starting load by 10%, but would check w/ manufacturer. Other folks may have advice for you.

  3. mseric

    mseric New Member

    You will be fine, just start your load work at the "Start" charge and work up. No need to go below Start.
  4. Rick1967

    Rick1967 Well-Known Member

    I use mag primers for everything. I just use the starting load in the book.
  5. BillM

    BillM Active Member Supporter

    I see a 10-15 fps increase in velocity with small pistol magnum. If you are
    running a striker fired gun you may or may not have issues with light strikes.

    When I was loading for 9mm minor, 9mm major, 40 minor and 40 major for
    USPSA competition, I used Winchester SP magnum in everything--but ran
    a stock striker spring in my Glocks. No problems.
  6. samnev

    samnev New Member

    That's exactly what I did with the magnum primers. Then work your way up very slowly. IIRC I ended up using about 10% less powder that what I had been using.
  7. JonM

    JonM Moderator


    the issue with magnum primers in very small charge weights is over pressure. there is so much energy coming out of a magnum primer its possible to get detonation instead of a controlled burn.

    on the other hand since the charge weight in a 9mm is so small you probably wont notice it if it does.

    if your getting flattened primers in a 9mm your pressure is too high.

    cratering: where the primer metal is flowing into the firing pin channel


    flattened primer. not necessarily sign of over pressurein some cartridges. but in a 9mm it is the primer has flattened and totally filled the primer cup.


    none of these are ways to measure pressure. they are merely indicators you need to back off.