7 saum unexpected velocity

Discussion in 'Long Range Hunting & Shooting' started by XTRTITAN, Apr 8, 2012.

  1. XTRTITAN

    XTRTITAN Active Member

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    I have a 7 saum with a 26" critirion on a savage pta. I am getting 3150 fps shooting berger 180 hibrids over 54.5 grains of h4350. The combo shoots .5 at 100 but is showing lots of vertical at distance. I am using cci 250 primers and wondering if it would be better to used standerd primers or would it be better to reduce the charge until i get the 2950-3000 fps range that everybody seems to be using. Any help is greatly appreciated as range time is limited. Thanks in advance
     
  2. elkaholic

    elkaholic Well-Known Member

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    That sounds AWFULLY high! Are you sure your chrono is giving you correct velocity?......Rich
     

  3. XTRTITAN

    XTRTITAN Active Member

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    I am using the trajectory for velocity. It takes 21.5 moa to reach target at 1035 yds with a 100 yd zero. Havent had a chance to chrony it yet but with the jbm program this gives me a velocity around 3150.
    I cant believe i am getting that trajectory with a 26 inch tube. I dont think the velocity is stable because of the vertical i am seeing. I will get the chrony out and double check the velocity asap.
     
  4. elkaholic

    elkaholic Well-Known Member

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    I think that explains it. That velocity sounds near imossible to me! Something is likely wrong with data input. Let us know what the chrono reads.......Rich
     
  5. trueblue

    trueblue Well-Known Member

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    Agreed.cannot get that kind of velocity out of a 7SAUM w/the 180's. and a 26" barrel.
    You are into 7-300WM territory now.
     
  6. liltank

    liltank Well-Known Member

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    You need to find out what your extreme spread is also. Sounds to me if you are getting a big vertical dispersion that you have a big ES. Changing your primer to a large rifle might help to calm that down some. It will effect your velocity too. Pressures should be lower also. You'll definitely need to use a chrony to see what your numbers are.
     
  7. jabey9210

    jabey9210 Well-Known Member

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    Maybe the actual bc of the bullet is off a bit cause you can change the bc on jbm to get your correct trajectory also. I shoot a 7mm Wsm and get exactly 3000 fps out of a 27" tube with 180 berger vld's according to the chrono and with that my trajectory is right on with jbm I thought they were pretty hot loads but I'm on my 6th reload on this brass so they must not be too bad. But out of my 243 if I go with the chrono and jbm they are off so since I know the chrono is pretty accurate I change the bc and get the correct trajectory if I changed the fps it says I'm shooting about 200 fps faster than I actually am so either way as long as your trajectory is right on the numbers in jbm are just that and really don't matter as long as the trajectory lines up!!! I also agree with checking your extreme spread if you're having vertical issues!!
     
  8. XTRTITAN

    XTRTITAN Active Member

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    Shot some 162 amaxs i had loaded over the chrony today and got anywhere from 3160 to 3295. This is with 56.0 grains of h4350 and cci 250 primers. It doesnt seem like there is any sign of high pressure. No hard bolt lift and the primers still have nice round edges. This load is decent at 100 but obviously wont work with distance. I am planning to try some regular primers any try to get the extreme spread under control. Not sure if the keg of powder i have is giving me the extra speed or if it is the barrel. I have not tried any other powders with this gun yet.
     
  9. elkaholic

    elkaholic Well-Known Member

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    With spreads like that, I would still be suspicious of the chrono.....Rich
     
  10. rscott5028

    rscott5028 Well-Known Member

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    Your data doesn't add up.
    You may have multiple problems... with JBM and/or the chrony
    e.g. Scope height, 100yd zero, scope clicks, powder scale, chrony itself

    If you throw out your cold bore/fouling shot, what was your ES and Standard Deviation? i.e. were the chrony readings all over the place? Or, just one or two outliers? ...perhaps muzzle blast too close to the chrony

    How many shots did you record and were they all within a short period or throughout the day?

    Did lighting change e.g. clouds vs sun during the chrony session?

    Are you letting some of the cartridges sit in the sun or hot chamber which would increase MV?

    Do you have a known good load/rifle to fire across the chrony as a baseline?

    -- richard
     
  11. XTRTITAN

    XTRTITAN Active Member

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    I will try to shoot some 180s across the chony today. I will bring my 6mm dasher to shoot and make sure my chrony hasnt went bad. I will post the results when i get them. Thanks for the help everyone
     
  12. the shotty

    the shotty Well-Known Member

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    How far was your chrono set up? When I first got my chrono I didn't know it was supposed to be 10 ft away from the barrel and was gettin 4700 fps with 140 gr amax in my .260.
     
  13. XTRTITAN

    XTRTITAN Active Member

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    I think i am getting closer to finding my rifles happy place. I set up today with the chrony at 10ft from the muzzle. I brought my 6 dasher as a baseline for the chrony speeds. It shot a nice little ragged hole with velocity for 5 shots being 3083,3086,3097,3071,and 3068. This is normal for this gun and the jbm trajetory matches these numbers well.

    Now for the 7saum.i loaded 5 180 vlds at the original 54.5 grains of h4350 and the velocitys were 3057,3000,3093,3123,and 3118. These produced a 100 yd group around 3/4".

    I also loaded 5 180 vlds with 52.5 grains of h4350. The velocitys came in at 2941,2923,2917,2919,2953. This produced a 3/8 inch ragged hole a 100 yds. Extreme spread of 36. I had 5 more rounds at 52 grains with almost identical results.

    This seems like a lot of speed for 52.5 grains of powder but if the trajetory matches it i guess that will be ok.

    Would you guys accept an extreme spread of 36 or change primers or any other tricks to lower the extreme spread? Accuracy seems to be good here. I really dont want to wear this barrel out before i get it tuned.
     
  14. XTRTITAN

    XTRTITAN Active Member

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    P.s. All above loads were shot with cci 250 primers.