Twist, Barrel Length, Bullet Weight

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  • SevernBob

    It's All Boogered Up
    MDS Supporter
    Dec 17, 2012
    462
    Severn
    I know. Another one. It's either all the variables involved or my thick head because this isn't sinking in very well. There's a lot of good info in the threads linked further below. Thanks to all for the good reading.

    So, I found this calculator (yeah, probably a dupe), but it seems to conflict with the chart Crab Bait posted. Of course, that chart doesn't appear to factor in bullet length and I'm not sure what barrel length is assumed.

    http://bulletin.accurateshooter.com...-twist-rate-with-berger-stability-calculator/

    I used this picture for bullet lengths. Not sure how accurate it is.
    http://www.bevfitchett.us/rifle-marksmanship-m16a1/ballistics.html

    Does the calculator seem accurate to you? Is there such a thing as too high SG?


    OTHER THREADS
    http://www.mdshooters.com/showthread.php?t=82517&highlight=twist



    http://www.mdshooters.com/showthread.php?t=101251&highlight=twist

    This is just info from the net, but I thought enough of it to save it... others may shoot it down.


    http://www.mdshooters.com/showthread.php?t=69369&highlight=twist
     

    SevernBob

    It's All Boogered Up
    MDS Supporter
    Dec 17, 2012
    462
    Severn
    Here are the inputs I used on the calculator.

    Caliber .224 inches
    Bullet Weight 55 Grains
    Bullet Length .76 inches
    Barrel Twist 7 Inches/Turn
    Muzzle Velocity 3100fps
    Temperature 70 F.
    Altitude 100 Feet

    It shows SG = 3.75, which is well into the "Comfortable Stability" range that starts at 1.5. The chart posted above indicates that 55gr in a 1:7 is not the best or not as good as it could be. I just don't know what to make of that.
     

    stu929

    M1 Addict
    Jan 2, 2012
    6,605
    Hagerstown
    From some very veteran loaders I've met they said bullet length has a ton to do with stability and spin rate which the graph you have doesnr account for. For a quick and dirty reference chart I think it works well but there will always be exceptions to this.
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    Bullet length is the actual parameter that sets the required twist along with muzzle velocity.

    Bullet weight is only indicative, in that heavier bullets in a given caliber are typically longer.
     

    BradMacc82

    Ultimate Member
    Industry Partner
    Aug 17, 2011
    26,177
    will the barrel has what the twist is stamped into it? i mean i remember what mine is from the description when i bought if but some may not remember.

    Generally, yes.

    Although I have seen (rarely) barrels w/out info stamped.
     

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