muzzle velocity inconsistant

Discussion in 'Reloading' started by GoArmy, Jul 10, 2011.

  1. GoArmy

    GoArmy Active Member

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    I just started reloading and I'm having trouble with my velocities jumping around, 7 mm REMmag. I'm getting up to 100 fps difference. What gives. I have digital scales, and I'm trying to get the powder load to within a 10th of a grn, but I must be doing something wrong,.
     
    Last edited: Jul 10, 2011
  2. bman73

    bman73 Well-Known Member

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    how close to the chrono is the rifle? also intermittent sun and cloud will sometimes give wacky readings. If the grouping is consistant I would say that it probably is more than likely the chronograph giving false readings. Hope this helps
     

  3. GoArmy

    GoArmy Active Member

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    I was a good fifteen feet away from the crony, and in a shaded area, I had the cronograph laying on the ground. This crony is like new.
     
  4. bman73

    bman73 Well-Known Member

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    is your POI consistant with this load setup or all over the place as well as the velocity?
     
  5. GoArmy

    GoArmy Active Member

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    The rifle yesterday shot a 3/4 group at 100yrd with this batch of reload
     
  6. bman73

    bman73 Well-Known Member

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    I would try moving the chronograph out a bit further then, that sounds like it's too consistent to have a spread of 100fps to me. I have in the past had to set a chrono out as far as 25' to get a proper reading that wasn't being affected by the muzzle blast
     
  7. GoArmy

    GoArmy Active Member

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    You may be on to something there, the 7 mag throws a hell of a blast, and I was doing this on dusty gravel, and I had the crony sitting on the ground, and I was also.
     
  8. bman73

    bman73 Well-Known Member

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    if possible maybe try to get it up off the ground as well to try to eliminate both muzzle blast and dust. With the grouping your getting I would definately try with the chronograph before you change anything with the load, sounds fairly accurate to me.
     
  9. GoArmy

    GoArmy Active Member

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    Thanks, I'm going to change the entire setup next time, Get off the gravel and do this in my field, set the crony on a table, The rifle really shoots well, but with the crony reading all over the place, i dont want to calculate my long range hold overs till i get the MV steady, I have been using the G7 Calculator on the Vortex Optics Web site.

    My cartridge set up is 7 MM Rem, Winchester Brass, Fed gold medal match Primers, H-4831, 65 gr. Berger 168 VLD, OAL 3.030. I may stretch them out to 3.042,
    I have also used PMC Brass. Not sure about that brand.
     
  10. bman73

    bman73 Well-Known Member

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    I used PMC many years ago on a Mauser 7x57, just used it to plink with though, just an old iron sight gun so I can't comment on it's accuracy as I never really did try to hard with it. Still have the brass actually 15 yrs later but it hasn't been used in almost 10. Good luck with yoyr set up and I hope I was of some help to you
     
  11. boomtube

    boomtube Well-Known Member

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    "I'm getting up to 100 fps difference. What gives."

    Actually, that's not bad unless you plan to shoot passed maybe 500 yards.
     
  12. GoArmy

    GoArmy Active Member

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    I want to go out to 750 yrds, so I would like to get the velocities pretty close, Thanks for all the info.