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Thread: Difference in point of aim

  1. #1

    Difference in point of aim

    Hi folks,
    Just a quick question my 75grain Vmax bullets for my .243 shot point of aim at 100 metres, however 100gn spbt shot an inch and a half high at 100 metres, even though they are traveling approximately 170 fps slower. Logic would suggest that it should be the other way around or is my logic all to shot.

    cheers in advance

    Jason

  2. #2
    Possibly, and Im just guessing here so don't laugh at me , because the 100Gn SPBT has a slightly higher Ballistic Coefficient than the 75gn VMax?

    According to my Hornandy Manual :

    75gn VMAX B.C. 0.330
    199Gn SPBT B.C. 0.405
    Last edited by WiltsPat; 06-07-2010 at 10:27. Reason: I cant speel

  3. #3
    Weight has nothing to do with this, it is all about barrel harmonics.

    The 75gr bullet is exiting the barrel at a different (presumably lower) point in the barrel's vibration cycle than the 100gr.
    Brian.

    Just because you are paranoid, doesn't mean they aren't out to get you......

  4. #4
    its all about where the bullet leaves the barrel on the figure of 8 created by the harmonics. best place for it to exist is at the top or bottom where the barrel is slowing to change direction - apparently

  5. #5
    Quote Originally Posted by monty View Post
    Hi folks,
    Just a quick question my 75grain Vmax bullets for my .243 shot point of aim at 100 metres, however 100gn spbt shot an inch and a half high at 100 metres, even though they are traveling approximately 170 fps slower. Logic would suggest that it should be the other way around or is my logic all to shot.

    cheers in advance

    Jason
    Could be harmonics, but I'd guess recoil energy. The slower, heavier bullet recoils more and is traveling slower than the 100 grain bullet so the angle of departure of the bullet from the barrel is higher in the recoil cycle. You see this illustrated all the time in handgun shooting: the lighter the bullet, the lower the point of impact. Try a different kind of rest (bags from a bench VS bipod or sticks) and see if the results change.~Muir

  6. #6
    I have a 6.5x55 that was a stutzen so has a shortish thick barrel and with most bullets homeloads and factories in 100gn 120 gn and 140 gn they all shoot to the same point of impact give or take at 100yds.
    Keith
    PS It has been un-stutzened by having the front of the stock shortened to sporter length and floated
    AT THE AGE OF 50 I DECIDED I WAS GOING TO GROW OLD F***ING DISGRACEFULLY

  7. #7
    Cheers gents for the replies, I will try from a different rest Muir when out next and see if it makes a difference.

    Thanks again

    Jason

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