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Thread: drop in fps

  1. #1

    drop in fps

    Last weekend I popped out and zerod my 308 with its new scope. Over the chrono a 5 shot string averaged 2750 fps there was a 40fps spread over the 5 shots lowest 2725, 2734, 2752,2763, highest 2765. That was a 150 gameking with 45 grns varget. I also tried 45.5 and 46grn loads. Now the 45.5 shot under an inch group so I decided to run my last 2 over the chrono. Now I know 2 shots will not give an average but I was surprised when the 1st was 2750 and the other 2711. What do you believe could be the cause of the poor speed load??

    Now before I get lynched asking about speed Ive Swaro Z3 with a brx reticle. So I believe an acurate average is well worth knowing..


    Nutty

  2. #2
    Quote Originally Posted by nuttyspaniel View Post
    What do you believe could be the cause of the poor speed load??
    Not that you can tell much from a 5-shot string, either - but given that from that string the spread was 40fps, and the difference between your last two shots was 39fps, it's probably reasonable to say the lower-velocity shot resulted from a combination of circumstances relating to the load, the rifle and the chronograph - and all within normal limits.

  3. #3
    Quote Originally Posted by nuttyspaniel View Post
    Last weekend I popped out and zerod my 308 with its new scope. Over the chrono a 5 shot string averaged 2750 fps there was a 40fps spread over the 5 shots lowest 2725, 2734, 2752,2763, highest 2765. That was a 150 gameking with 45 grns varget. I also tried 45.5 and 46grn loads. Now the 45.5 shot under an inch group so I decided to run my last 2 over the chrono. Now I know 2 shots will not give an average but I was surprised when the 1st was 2750 and the other 2711. What do you believe could be the cause of the poor speed load??

    Now before I get lynched asking about speed Ive Swaro Z3 with a brx reticle. So I believe an acurate average is well worth knowing..


    Nutty
    I do a lot of chronographing. Your sample of five shots is too small to determine much but the two you fired falls close to the 40 fps extreme spread you got for the initial five shots. It would probably hold true for the two you fired at the end, as well. Considering it was only two shots, there really isn't much to say about it. If you'd fired 20 shots with that 45.5 load you might have found that the low was an anomaly that didn't effect your standard deviation by much.

    If you want to tighten that spread, try the Lee Factory Crimp Die. Works wonders.~Muir

  4. #4
    Quote Originally Posted by Muir View Post
    I do a lot of chronographing. Your sample of five shots is too small to determine much but the two you fired falls close to the 40 fps extreme spread you got for the initial five shots. It would probably hold true for the two you fired at the end, as well. Considering it was only two shots, there really isn't much to say about it. If you'd fired 20 shots with that 45.5 load you might have found that the low was an anomaly that didn't effect your standard deviation by much.

    If you want to tighten that spread, try the Lee Factory Crimp Die. Works wonders.~Muir
    Cheers Muir I am crimping. I may be looking too much into this and over complicating but the 2750 I can live with in a stri g but to drop to 2711, 14fps slower than the slowest with 45grn with an extra 1/2 grn thats my puzzlement...

    Daula perhaps.

    Nutty.

  5. #5
    Quote Originally Posted by nuttyspaniel View Post
    Cheers Muir I am crimping. I may be looking too much into this and over complicating but the 2750 I can live with in a stri g but to drop to 2711, 14fps slower than the slowest with 45grn with an extra 1/2 grn thats my puzzlement...

    Daula perhaps.

    Nutty.
    You're crimping and still getting 40 fps ES? That surprises me. Are you trimming to a uniform length at each loading??

    That low velocity?it's hard to tell what happened. Shoot more! ~Muir

  6. #6
    Quote Originally Posted by Muir View Post
    You're crimping and still getting 40 fps ES? That surprises me. Are you trimming to a uniform length at each loading??

    That low velocity?it's hard to tell what happened. Shoot more! ~Muir

    Yip Muir a head scratcher all trimmed etc.. But I may have solved it..... Ill report back if Im correct..


    Nutty

  7. #7
    Changed brass. Im on new lapua now. 45.6grn varget 20 thou of lands..


    Gave this at 2770 fps. Its .670ish edge to edge..

    Click image for larger version. 

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    nutty

  8. #8
    Seems you got it licked. (Ditch that piece of junk.)~Muir

  9. #9
    Quote Originally Posted by Muir View Post
    Seems you got it licked. (Ditch that piece of junk.)~Muir
    I here what your saying bro.. A better nicer trigger will help tighten the group...

    Nutty

  10. #10
    Quote Originally Posted by nuttyspaniel View Post
    I here what your saying bro.. A better nicer trigger will help tighten the group...

    Nutty
    Yeah...rubbish, look how far off the red spot you hit. I will solve all your problems and worries by buying that rusty old fence post off you for 20. Another example of SD charity at work!!

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