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Thread: Last minute reprieve

  1. #1

    Last minute reprieve

    All our club range days, for opportunities that would suit me, to zero large calibre un -modded rifles, were cancelled due to military needs. So I'm off with Mike this afternoon, down to one of his bigger less populated areas to enjoy the boom, & check zero some fresh reloads, for next weeks outing to a place where there may be some deer about!, just hope the rain doesn't run down my collar!.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

  2. #2
    And what a load of rubbish the shots turned out to be!!! Limited time to get things right, so finished up last night behind my place, in a howling gale, with three nicely grouped rounds inside a twenty mil square @ 100yds,BUT ONLY WHILE USING THE MODERATOR!..... must be a barrel harmonics thing.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

  3. #3
    Sounds like it's time to try OBT.

    There was a chap who joined the forums that is well into this and has gotten quite good results working it out as a starting point but I am sorry to say some didn't like his views on some things and made it unpleasant so he left these forums. If you think it might be of some use let me know and I will try to hook you up with him via the web.

  4. #4
    Optimal Barrell T................?
    Just guessing here.
    I can speak in-depth and with great knowledge about most subjects until some bugger who actually knows what he is speaking about opens his gob .

  5. #5
    Quote Originally Posted by Brithunter View Post
    Sounds like it's time to try OBT.

    There was a chap who joined the forums that is well into this and has gotten quite good results working it out as a starting point but I am sorry to say some didn't like his views on some things and made it unpleasant so he left these forums. If you think it might be of some use let me know and I will try to hook you up with him via the web.
    ​Kev, dont be one of those people who throw the odd French or Latin phrase in to sentences and then wait for someone to ask what itmeans. What is OBT?
    You can't say muntjac without saying, Mmmmmm.

  6. #6
    SD Regular willie_gunn's Avatar
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  7. #7
    SD Regular willie_gunn's Avatar
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    willie_gunn

    P.S. personally I just use standard factory ammo in my .243 and good old 150gr Nosler BT's on top of 43.5 grains of N140 in my .308. Harmonically speaking, the deer fall over just the same if you hit them in the right spot, but perhaps they would make a slightly different sound if I had tuned the load for OBT
    O wad some Power the giftie gie us to see oursels as ithers see us!

  8. #8
    Quote Originally Posted by Harry mac View Post
    ​Kev, dont be one of those people who throw the odd French or Latin phrase in to sentences and then wait for someone to ask what itmeans. What is OBT?
    Sorry I thought most who knew about hand loading were aware of this. As pointed out it's Optimal Barrel Timing.

    Basically is't working out the timing of the bullets exit from the muzzle and gettign it as close to the end of the arc as possible when the barrel is almost stationary. I am assuming you know that the barrel's muzzle whips in an arc!

    So as it changed direction to got back through the arc the barrel in momentarily stationary and if oen can time the bullets exit to this point of movement then the best possible grouping should be achieved.

    First one measures the barrel length from breech face to muzzle then one measures case capacity. Barrel profile.......i.e thinckness comes into i seem to think .. Anyway it's then a mathematical process to work out the timing of the "Node" and workign out the best powder and charge to obtain this.

    My American friend who got me slightly interested in this is a scientist by profession and inkling hence it's bread and butter to him. he not only has the desire but has invested in the computer software to help him work out these things and also he bought a "Pressure Trace" system to measure chamber pressures. He was designing his own cartridges for a specific purpose and building his own rifles. me I have enough trouble using a computer let along delving into programming but for him it seems to be second nature.

    Hope that helps a little.

  9. #9
    SD Regular willie_gunn's Avatar
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    Quote Originally Posted by Brithunter View Post
    Basically is't working out the timing of the bullets exit from the muzzle and gettign it as close to the end of the arc as possible when the barrel is almost stationary. I am assuming you know that the barrel's muzzle whips in an arc!

    So as it changed direction to got back through the arc the barrel in momentarily stationary and if oen can time the bullets exit to this point of movement then the best possible grouping should be achieved.
    To reinforce Brithunter's excellent summary provided above, here is a video of barrel whip. I know it's an old video that many have seen already, but it illustrates the point perfectly.



    So OBT is about finding the right load that will ensure the bullet consistently leaves the barrel when it is at a stationary point in the arc (e.g. when it is 100% straight). Apologies to the purists if I have misinterpreted or missed out all the natty science.

    willie_gunn
    O wad some Power the giftie gie us to see oursels as ithers see us!

  10. #10
    First time I've ever heard of this - but I thought that the bullet left the barrel before all the flames etc came out? I only ask as to me with that rifle it looks like the barrel is only bouncing about after the round has left the muzzle and the bolt is starting to open.

    I am not 'having a go', just curious as like I said, I dont think I've heard of this previously, but am looking at 'rolling my own' now I have a press and whatnot.

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