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bullet weight vs. twist rate.

Discussion in 'Rifle Country' started by RedAlert, Aug 19, 2006.

  1. RedAlert

    RedAlert Well-Known Member

    I'm curious. After a search of the archives, I didn't find any formulas to calculate the best rifling twist rate for a particular bullet weight.

    I'm particularly concerned with purchasing the right ammo for my .223 Mini-14. Would the heaver 62 grain NATO spec round be okay, or should I stick with the lighter 55 grain consumer spec ammo?

    Any help, is appreciated.

  2. mc223

    mc223 Well-Known Member

    Bullet Diameter squared X 150 divided by the length of the bullet. This is the Geenhill Formula. It will get you in the ballpark. Isnt the twist of the Mini like 1 in 12? If so the lighter-shorter bullets would perform better. Your rifle may shoot everything good or not.
  3. vesmcd

    vesmcd Well-Known Member

    I hate to be a killjoy, but mini-14's are pretty much known as "minute of pie plate" rifles at 100 yards with ammo they like. Sometimes you find one that will shoot a decent group. Long ago I had an early(180 series/scoped) that would shoot 1.5" groups at 100 yards with 52gr fmj. Didn't like anything else.
    Just keep in mind that the Mini-14 has a skinny barrel that throws bigger groups as it gets hot.
    Bottom line: try lots of different ammo until you find what works best. Hope you got a good one.
  4. RedAlert

    RedAlert Well-Known Member

    I'm not a hard core guy like most of you.

    I just want to get good plinking ammo for the moment. Eventually I'll invest some money in a new barrel and cinch up on the accuracy.

    Not be too much of a killjoy either, but a recent outing at the range proved that maintaining 4-5" at 100yds was no problem. Off a rest, I maintained 3", 5 round groups. I realize its not a tack driver, but as I stated, that wasn't my purpose in its purchase. A check of the Ruger Web site and the rifle's specs indicate that the stock twist rate is 1:9 in an 181/2" barrel.


  5. Red Tornado

    Red Tornado Well-Known Member

    With a 1 in 9, you should be pretty much good to go at least up to 69gr, and possibly 77gr. Apparently some will, some won't. My Savage is 1 in 9, and the 69 gr shoots best,(I 'think' this is the optimal weight) but the 55gr WWB will still shoot MOA, and I even shot some really good groups with some 45 gr varmint ammo.

    Basically, for a plinker, just about anything will work with that twist rate. If you're not trying to zero tiny groups, shoot what's cheap and has acceptable accuracy. Like you said, it's for plinking. Taketh thyself forth and plink!
  6. trueblue1776

    trueblue1776 Well-Known Member

    The Ruger plant completely retooled the Mini-14 line around two years ago. The rifles are much tighter now and post very respectable MOA (1.5-2.0 I believe is the claimed MOA). Definitely good for a SUR or Sport Utility Rifle. My personal best with a new mini is a hair over 2.5 in (Black Hills 55gr.), and I am not an experienced or talented rifleman.

    BTW "minute of pie plate" is an insult to a fine American rifle, I would have just bought another ROMAK if that was true.

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