Downrange Chrono vs Computer generated velocities

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Ian M, Oct 14, 2002.

  1. Ian M

    Ian M Well-Known Member

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    Here is an interesting list comparing my recent downrange Oehler velocities with the info from the latest Barnes reloading manual.
    .308 Win. 45.5/Varget 26" Mike Rock Barrel
    Yds Barnes Chrono'd
    Mzl 2600 2608
    100 2412 2428
    200 2233 2209
    300 2063 2050
    400 1901 1919
    500 1748 1763

    The Barnes book provides a pretty good indication of downrange velocity if you don't have a chronograph and go to the bother of shooting through it downrange.
     
  2. Len Backus

    Len Backus Administrator Staff Member

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    Ian

    I think somewhere I got the idea that BC's actually vary depending on the stability of the bullet as it leaves the tip of the barrel. Therefor, a certain bullet design may exhibit different BC's in different rifles or with different load parameters in the same rifle. Have you any thoughts on this?
     

  3. Ian M

    Ian M Well-Known Member

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    Len,
    Velly intelesting... but I must admit to being a trigger-puller first and foremost and haven't got a clue about the theoretical stuff. That is why I hang out at your site, hopin' to learn some of that magic, eh! (a little Canadian content there)

    Will leave the Ballistic Co-efficient stuff to the folks who enjoy or need it. I just want to make first shot hits, clang lots of steel and enjoy a bunch of shooting and hunting while we still can.

    For some dumb reason I distrust the tables and computer generated figures. I prefer to shoot actual drops and get actual velocities. Sure like to have actual drop figures and charts for my hunting rifles.
     
  4. Len Backus

    Len Backus Administrator Staff Member

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    I agree. I always rely on my own field-generated drop tables. I do however, rely on the "official" BC for guessing at wind drift.
     
  5. Jon A

    Jon A Well-Known Member

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    Great info, Ian!

    What elevation are you at? What was the temp that day? We "BC freaks" need to know the details....

    [​IMG]
     
  6. Ian M

    Ian M Well-Known Member

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    We are at 1890 feet above sea level and the temp was in the mid 40's.

    Load was .308 Win., 168 Barnes XLC, BC is .476 according to Barnes manual, 45.5 Varget in a BHA match case, Win. primer, O.L. was 2.83", 26" Mike Rock barrel.
     
  7. CAM

    CAM Well-Known Member

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    Very Very Interesting. I understand most of the BC stuff with the standard being. Sea level, temp 59 deg, BP 29.53, RH 78%. My question is this. The listed muzzle velocity will be the same at sea level as at 10,000 ft.? I do not have a chono at this time (on the wish list) so do I use the listed muzzle velocity and correct everything with the MAGIC B.C.
    Keep up the good info and good luck to every one hunting. [​IMG]
     
  8. kraky

    kraky Well-Known Member

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    I BELIEVE the idea about bullet stability affecting bc is DEAD ON. They recently did a test in Shooting Times comparing drop of round nose bullets to spitzers. The round noses seemed very accurate out to 300 yds. I played around with my computer program and found the round noses hit pretty much where they should but the spitzers dropped more than they should. One comparison was a round nose against a match king. At 300 yds they hit within 1" of each other. The only thing I can conclude is the match king was wobbling on it's way to 300 yds and the round nose was flying "tight".
    It all just goes to prove you really have to try those loads for accuracy and drop out to a minimum of 300 yds for average hunting conditions. Better yet even further for you guys and your ultra long range shooting.
     
  9. CAM

    CAM Well-Known Member

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    I think I have answered my own question. the B.C. is mostly External and powder charge muzzle velosity is Internal Ballistics. Muzzle velocity is more dependant on how sensitive the powder is to temp. Do the reloading manuals use a standard temp for muzzle velocity ?
     
  10. Brent

    Brent Well-Known Member

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    Ian,
    with those velocities being so close to the predicted Barnes data, does the drop they indicate follow yours as well or are the bullets falling much faster than Barnes says they do? I have found their BCs to be quite overstated in my tests so far, which was a disappointment.
     
  11. Ian M

    Ian M Well-Known Member

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    Brent,
    Good question. I just put the following chart together to try to find you an answer. They stay close out to 300 and then my drop figures are less than their computed figures. I expect that this would get more significant as the range extended.

    Distance Drop Barnes Drop
    Muzzle - -
    100 0 0
    200 4.0" 4.48"
    300 15.0" 15.95"
    400 28.0" 35.6"
    500 57.5" 64.84"

    All the more reason to shoot your own drops for the distances that we hunt to. I just know that these are the best shooting Barnes bullets that I have ever used, they hold together very well and they killed a couple of deer very cleanly so far.

    Hope you and your family are well and that everything is going OK up there in God's country.
    ian
     
  12. Brent

    Brent Well-Known Member

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    Ian, your doing about axactly the same to 500yds as my sons 308 with 150 XLC's at 2850 are in that 20" tube of his but with more energy ta boot. His is running 47.5gr Varget at a 2.85" oal and it groups between 3/4 and 1 1/4". Any other charge wt. and groups go to between 2 and 3+ inches. Pressure is running between 58500 and 60,000 psi so it's grouping well at top velocity unlike most of the other loads I have for it.

    I hit some of that 3/8" T-1 steel plate with the 308 Savage Striker during hunting season. The 165gr bullets just left a good mark on it with the back of it just deforming slightly is all. I never used the rifle on it though, but would recommend 200 yards for it if you wanted it left in mint condition with just marks only. My fathers 300WSM Rem700 put 180's clean through it at 100yds, so 300 yds maybe the limit there with the T-1 steel. Step in closer if you don't mind beatin em up a little.

    All is well up here and do you believe this, it's +48 deg F, STILL! It was down to 18 deg one night and then back up to the current temp. No snow yet just some rain about half the time.

    No moose in the freeze this year, the last two weeks were bad weather and animals were almost non existant. Bear was tracked a couple times but no luck, he was about maybe 9' probably just shy of it though. We got close one night, his tracks were over our foot tracks in less than the ten minutes it took us to get water from the creek and about 100yds away from the fill up spot. On the way back we must have been right on him.

    This was about 200yds away from a friend of mines cabin. The dog wouldn't leave our side, she just got real scared and was like glue just before we saw his prints. There was another moose kill about 75 yds behind the cabin and that night it disappeared compleatly!

    My friend Don thinks his 7 mag is a tad small for what ever made those tracks and is looking for a 300rum now, oh and no more going to the creek for water in the dark unarmed anymore for him just because its only 300yds away. It freaked him out a bit I think.

    Another thing, the best damn moose huntin vidio out there "Love Thunder and Bull II" has ours truely and his son right there in it, way to go Len and Andy. Check it out guys.