7mm Rem Mag Hornady 139 GMX Load Development

Discussion in 'Reloading' started by ovastafford, Oct 16, 2012.

  1. ovastafford

    ovastafford Well-Known Member

    Messages:
    938
    Joined:
    Oct 23, 2009
    So Im working up a load for my Rem 700 7mm Rem mag with the Hornady 139gr GMX using Hornady cases, Rem 9.5 mag primers, 4831sc. I loaded them up 50 thousandths off the lands starting at 63grs working up in 1 grain increments monitoring velocity and pressure signs. I got pressure signs at 66 grains so I stopped there. I then shot 5 shot groups with 63-64-65 grains. My groups ranged from just over 1" to 2". Velocities were very consistent, so now I guess ill play with seating depth and see if that tightens things up a bit. My question is how much should I vary my seating depth? Ten thousandths, Twenty, Thirty??? Also my average velocity was 2,997 at 63 grains, 3,046 at 64 grains and 3,090 at 65 grains. According to the Hornady manual max is at 65 grains at 3,000 fps and Hodgdon Manual says 68.8 grs at 3,054 fps. Should I use 64 grains as max considering the velocity?

    Any help is appreciated!
     
  2. Lefty7mmstw

    Lefty7mmstw Well-Known Member

    Messages:
    4,280
    Joined:
    May 13, 2012
    I'd go with the highest charge with accuracy that shows no pressure signs. Man, I get 3100 fps with 4064 in my 7mag with a 140 sierra and 3100 fps with a 130 gmx with I 4831 in my 270 win, so 4831sc isn't doing you any favors.
    I am 25 thou. off jamb in my 270 with the gmx 130.
    Why don't you finish up your 4831 and try out some rl22 in that 7mag. I've been using it for years in 7mags. You should net 3200 fps with it using 68-70 grains with a 139-140 grain pill and a mag. primer. Work up of course.
     

  3. g0rd0

    g0rd0 Well-Known Member

    Messages:
    517
    Joined:
    Mar 9, 2012
    in the past my fav powder for rem. 7mm mag was imr 7828 and for my hunting bullets (150 grn e tip, fed. cases cci mag primer and 67 grn imr 7828) I like the results so I stick with it.
    But, for plinking and easy recoil at the range I use 139 grm hornady sp fed. case win std primer and 47grn imr 3031 (3/4 inch groups at 100 yrd)
    I have recently aquired a couple hundred sierra 175 grn sp's and some rl22, after I burn off some already loaded 162 grn amax (my rifle is not fond of the amax, best group at 100 yrd 1&1/2 inches) I will try the 175's with the rl22 looking forward as I am hearing a lot positive results with the rl22 and heavy bullets.
    If my rifle does not perform well with the 175's then I will just stay with the 139's at the range and the e tips in the field
     
  4. ovastafford

    ovastafford Well-Known Member

    Messages:
    938
    Joined:
    Oct 23, 2009
    Thanks for the suggestions. I don't really care for Reloader powders much because of their temp sensitivity. Where I live its 90-100 degrees right now and where Im going hunting it will be sub freezing so there will be a big difference in velocity. I think what Im going to do is load some up at 20 thousands off, 40 thousands off, 70 thousands off and 90 thousands off and see which one groups better.
     
  5. Lefty7mmstw

    Lefty7mmstw Well-Known Member

    Messages:
    4,280
    Joined:
    May 13, 2012
    check out my location-- rl's about all I use-- it's really no worse than the "extreme" stuff in most rifles. I've killed deer at -20 and 80 degrees with the same rl22 load in my 300 win, and they died just as well and I didn't need to fiddle with sights. I use rl25 in the 7stw and it's been very good to me.
     
  6. ovastafford

    ovastafford Well-Known Member

    Messages:
    938
    Joined:
    Oct 23, 2009
    Ok Ill have to give it a try.