Velocity and BC?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Exhaust3, Oct 1, 2005.

  1. Exhaust3

    Exhaust3 Well-Known Member

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    I have a question regarding velocity. I don't have access to a chronograph and the velocities I have posted in the past are not accual readings, rather calculations. I have a 30-06 Ack pushing a 190gr SMK. Sierra publishes a BC of .533 for this bullet. I have made drop charts and for this particular rifle and everything I enter into ANY ballistic calculator gives me erroneous numbers. The reason I ask is either the BC is wrong or the velocity.
    For example: At my range I have a 40" rock at 1175 yds. I know that 30.5 MOA dialed in my scope will smack that thing every time. I know that at 875 yds., 16.0 MOA will smack the 24" silouette "dinger." I know that it only takes 5.25 MOA to hit the 500 yard target.
    So to get to the meat of the question, is the BC higher than published or am I pushing the SMK faster than what I think am?
    I live in Utah at 5300 ft. and the day I shot those targets it was 77* and 0 wind, I mean absolutely no wind whatso ever. I used Jacksonrifles.com ballistic program and to get to 30 MOA (1175 yds.)I had to enter 2950fps. but I was way off at 875 (18.73 MOA) and for 500 (7.81 MOA). I am confused, I guess I'll have to get a chronograph and quite bothering you all.
     
  2. sewwhat89

    sewwhat89 Well-Known Member

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    What is your zero range? I'll give it a shot.
     

  3. Exhaust3

    Exhaust3 Well-Known Member

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    Zero range, 100 yds,. I hope someone would.
     
  4. Guest

    Guest Guest

    well according to you..
    at 500 yards and 5.25 MOA your muzzle velocity needs to be 3450 fps..and that ain't happening with the 190 outta an '06ack
    at 875 you need 3225 fps
    at 1175 and 30.5 moa ...you need 2900 to 2950 fps and thats hot for an 06 ack..
    at 2900fps your 500 yard MOA is 8 your 875 is 19.50 your 1175 is 2900-2950...

    sumptin is screwy.. and 40" is over 3 feet.. so where are you hitting that rock???
     
  5. sewwhat89

    sewwhat89 Well-Known Member

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    [ QUOTE ]
    I know that it only takes 5.25 MOA to hit the 500 yard target.

    [/ QUOTE ]

    Something is very wrong.

    You would have to be shooting the 190SMK @ 3600 fps or so to do that. Double check your numbers?
     
  6. Exhaust3

    Exhaust3 Well-Known Member

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    That's what I am telling you. I know the numbers you have run are accurate, I've run them over and over myself. I figure that 2950 was pushing it, but nothing over 3000 for sure. But I can assure you I hit that 875 "dinger" with only 16.0 MOA!! I've hit "the rock" numerous times with only 30.5 MOA!! The rock, I can put them anywhere you want me too. I'm as baffled as you. I'm not trying to pull any strings, I shoot alot and this all baffles me as well. I dunno, I'm going to have to do something. Thanks for all your replys!!
     
  7. davewilson

    davewilson Well-Known Member

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    the only way to know is to shoot at those ranges with the scope set on 100 yd zero and measure your drop.you're going by how many MOA the scope says it's moving but i'll bet it's moving more than it says.
     
  8. Mysticplayer

    Mysticplayer Writers Guild

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    A couple of ways to check. At 100yds, put up a tape measure on a board. Zero the rifle at the bottom (shoot a rd). Dial up the scope and shoot at the different come ups. See where the bullets actually land.

    If the scope is off, you will quickly see. Example, you dial up 10 min but your actual bullet impacts 12 min high. The scope moves more then expected so it looks like your bullet is flying flatter then it actually does.

    If all the come ups check out, shoot at your favorite distances but on a MOA sized target. Shooting and hitting a 40" rock does allow for some degree of error (2MOA or more). If you shoot and hit a 11" target at 1100yds, well then you would have to say things are dialed in.

    Finally, what drag function are you using in your data. That is the G number usually required. Most programs default to G1 which is usually wrong for boattail bullets.

    If everything else checks out, change the G function but keep all other data the same. It might bring your data in line with real world observations.

    That is what I had to do with recent shooting of the 162gr Amax from 2 7RM. By changing the G function, I was able to get my data and real world come ups to agree.

    Hope this helps. Try and get yourself a chronie. Would reduce the amount of guesswork.

    Jerry
     
  9. Mikecr

    Mikecr Well-Known Member

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    What scope are you using?

    Peja's utilizes Ingall's retardation model. But checking with other software, your 5moa 500yd isn't right. G7 BC correction doesn't help either.
     
  10. Jon A

    Jon A Well-Known Member

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    Try measuring the actual "click" value of your scope. I'm guessing your particular scope simply moves more than 1/4 MOA for each click.
     
  11. Jeff In TX

    Jeff In TX Well-Known Member

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    Exhaust3,

    If you have access to a ballistic computer you can usually reverse engineer your data. However, you need good input data. The BC that Sierra advertises is a baseline, your gun with your load and velocity may change it a bit.

    When I see folks doing this, the biggest mistake in reverse engineering is the scope height. Most use a standard 1.5 inches that comes in the ballistic computers. You need to measure it and use the correct height.

    Then once you have all the input data, start playing with the BC until it closely matches your actual data. You won't get it exact, but you should be able to get close.

    Hope it helps,
     
  12. Mikecr

    Mikecr Well-Known Member

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    Did you "zero" your turrets at 100yds?
    You have to discount MOA needed for initial setup.
    If you haven't, that's your problem.

    I get a pretty good match using EXBAL(which is G1) when I set the zero to minimum for this program(25yds).
     
  13. jb1000br

    jb1000br Well-Known Member

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    Wow, saw 5.25 to 500 in the first post, and knew sumpin' aint right /ubbthreads/images/graemlins/shocked.gif

    The only time this has happened to me is when i was shooting over a dip in the terrain -- about a 25-30ft drop between me and the target.

    The wind was coming at me from about 1 'o clock and LIFTING the bullet when it hit the dip and flowed up and over.

    Got any terrain like this between you and the 500yd target?

    JB
     
  14. Exhaust3

    Exhaust3 Well-Known Member

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    I just thought I would update all that have replied to this post. First off, thank you for enlightening me to my dilema. Second, I have no idea what I was thinking. I posted this question w/o even giving a second thought as to what I should do.
    I scratched my head and decided that something was WAAAAY wrong and loaded up the rifle and gear and went to the range. Well to make a long story short, My firt shot was 6" high at 100 yds. Need I go on?? I didn't think so. Re-zeroed the scope and wouldn't you know, my ballistic drop tables were right all the time.
    Thank you all.