Quantcast
  1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Does rate of twist = your bullet weight ?

Discussion in 'Handloading and Reloading' started by brow_tines, Sep 28, 2011.

Thread Status:
Not open for further replies.
  1. brow_tines

    brow_tines Member

    Joined:
    Feb 14, 2011
    Messages:
    72
    Location:
    Kentucky
    I was talking to another reloader the other day and he said he based his bullet weight on his barrel rate of twist. Therefore he shoots 62 grain bullets through his 22-250. Any thoughts on this?
     
  2. redbullitt

    redbullitt Member

    Joined:
    Nov 9, 2008
    Messages:
    902
    Location:
    Morgantown WV
    Twist is going to determine what weight of bullet you can keep stable in given conditions.

    A 1/10 twist in 308 will stabilize a 175 vld, but a slower 1/14 twist will not, and therefore you will have keyholes and poor accuracy.

    For a .223 rem, I have a 1/9 twist. Usually I am going to run bullets lighter than 70 grains. YMMV of course.
    For a .308 win, I have a 1/11 twist. I have had good experiences with bullets up to 190 grains. It would probably do others too.
    For a .338 lapua, I have a 1/10 twist and am usually running a 300 smk.
     
  3. brow_tines

    brow_tines Member

    Joined:
    Feb 14, 2011
    Messages:
    72
    Location:
    Kentucky
    OK, so is there a formula or chart to figure out rate of twist and bullet weights ?
     
  4. redbullitt

    redbullitt Member

    Joined:
    Nov 9, 2008
    Messages:
    902
    Location:
    Morgantown WV
    Miller stability formula works well, google jbm ballistics. It will be on the bottom part of the page of calculators.

    There are also some generic charts that you can google up I am sure.

    Just seeing what other people are using successfully helps as well. Just remember that each rifle and conditions can be different.

    Easy way to test is to shoot targets (maybe 12 ft, 25 yd 50 yd 100 yd etc) at various distances. Inspect the bullet holes; if they are nice and round you are good to go. Oval, then not so much. Check out the holes at whatever range you may be shooting just to be sure.

    Easy way to find your twist is to mark a cleaning rod and run a patch down your bore. Measure how many inches it takes for the rod to make one full turn. If it takes 8 inches for one turn, then you have a 1 in 8 twist.
     
  5. cfullgraf

    cfullgraf Member

    Joined:
    Oct 19, 2010
    Messages:
    6,922
    Location:
    East TN
    The twist rate of a barrel determines what length bullet the barrel will stabilize. Weight is not part of the equation. There are a couple different ones out there.

    Conventional construction bullets, lead with a copper jacket, are pretty much the same length for the same weight. So a bullet weight can be associated with the appropriate length.

    With non-lead bullets (all copper or non-lead cores), the bullets will be longer for the same weight as a lead bullet and therefore may need a faster twist.

    The equations are not an exact science and several other factors come into play but bullet weight is not one of them.
     
  6. Strykervet

    Strykervet member

    Joined:
    Nov 16, 2010
    Messages:
    1,610
    Twist = (CD^2)/L X Sqrt(SG/10.9)

    The specific gravity of lead core bullets is about 10.9 so the second half goes away. For solid core copper bullets, substitute SG with the specific gravity of substance, 8.96.

    Then twist for lead core bullets is (CD^2)/L. C = is a constant, use 150 for under 2800fps, if over 2800fps use 180. For about 2800fps, I use 165. D = diameter of the bullet and L = length of the bullet. Almost all of this info is from Wikipedia.

    I use this information when I order a barrel from Satern. They can do rifling down to a thousandth of an inch. So I pick the bullet I intend to use the most and analyze it and get the twist rate this way. Then the barrel will be optimized for that one bullet, but will work fine with the others too. When you think about it, you can only have one optimized twist anyway, so if you have a barrel cut, get it cut to work best for what you plan on using.
     
  7. helotaxi

    helotaxi Member

    Joined:
    May 23, 2009
    Messages:
    2,218
    The idea of "best" is a complete misnomer. "Adequate" is the correct term. If the twist is fast enough to stabilize the bullet, you're good. Beyond that, you can stress about it and develop paralysis through analysis to no practical effect. Decide the longest bullet you plan on shooting and plan your rate of twist to stabilize that bullet with a bit of margin for changing conditions and then get a high quality barrel. It will shoot that long bullet and anything shorter.
     
  8. Fatelvis

    Fatelvis Member

    Joined:
    Dec 25, 2002
    Messages:
    1,848
    Location:
    Lockport, IL
    Cfull has it exactly correct. That's why one company's bullet will stabilize in a marginal twist barrel, when another company's bullet won't, even if they are both the same weight.
     
  9. USSR

    USSR Member

    Joined:
    Jul 7, 2005
    Messages:
    8,390
    Location:
    Finger Lakes Region of NY
    +1. The Greenhill formula and any other formula used to determine the correct twist for a particular bullet, simply calculate the theoretical "optimal" twist rate for maximal stabilization. There is a bit of leeway in regards to stabilizing bullets.

    Don
     
  10. Cemetery21

    Cemetery21 Member

    Joined:
    Oct 12, 2010
    Messages:
    287
    Location:
    MO
  11. 243winxb

    243winxb Member

    Joined:
    Jul 7, 2004
    Messages:
    8,657
    Location:
    Hopewell Big Woods
    Barrel Rate of Twist

    In .224 bullets, Sierra 69gr & Hornady 68gr Match have the required twist printed on the box. Sites like Berger has twist rates posted for each bullet. Sierra only for some that require a faster than normal twist. The velocity of a bullet in a given caliber has to have an effect? Compare 222 Rem. to 220 swift? Talking about length, the Hornady 68 is a lot longer then the Sierra 69gr match, takin up way to much powder space in the 223/5.56.
     
    Last edited: Oct 1, 2011
  12. jerkface11

    jerkface11 Member

    Joined:
    Oct 27, 2005
    Messages:
    5,498
    Location:
    Arkansas
    Yes with a higher velocity you can get away with a lower twist rate. After all the bullet doesn't know what rate of twist you are using. It's the RPM's that matter.
     
  13. Hondo 60

    Hondo 60 Member

    Joined:
    Sep 6, 2009
    Messages:
    5,256
    Location:
    Manitowoc, WI
    Even after finding the bullet weight that's supposedly good, you have to remember each rifle is different.

    In a .223, for instance, mine is a 1 in 9 twist.
    I've tried 50, 55, 60 & 62 grains.

    The 55 grain is far superior to the others in accuracy.

    In this case everyone's mileage WILL vary.
     
  14. ranger335v

    ranger335v Member

    Joined:
    Dec 3, 2006
    Messages:
    3,797
    "Adequate" is the correct term. If the twist is fast enough to stabilize the bullet, you're good.

    Well stated.

    It's impossible to do much figgering on twist rate alone, it's spin that determines stability and spin is a function of both twist and velocity.
     
  15. murf

    murf Member

    Joined:
    Nov 16, 2010
    Messages:
    2,922
    Location:
    arizona
    if the bullet shoots well in your rifle, shoot it. if it doesn't, don't shoot it.

    murf
     
  16. helotaxi

    helotaxi Member

    Joined:
    May 23, 2009
    Messages:
    2,218
    Velocity plays a part because pushing the bullet faster does increase the RPM of the bullet, but it also increases the upset force on the bullet requiring it to spin faster to remain stable.
     
  17. StoneColdKiller

    StoneColdKiller Member

    Joined:
    Oct 7, 2011
    Messages:
    4
    Location:
    Colorado
    I looked up my new .270 wsm.... Says 10" for ALL bullets...

    My Remington XCR 700 says it has a 10" twist... Sa-Weet!!!
     
  18. NoAlibi

    NoAlibi Member

    Joined:
    Jun 22, 2009
    Messages:
    500
    Location:
    Boca Raton, Florida
    Over Stabilization

    IIRC, Julian Hatcher stated in a book authored by him titled "Hatcher's Notebook" that a bullet can be over stabilized. If memory serves, the problem occurs when the over stabilized bullet reaches the apex of it's trajectory and resists going over point first for a period of time.

    I have the book, but it's currently in one of many unopened boxes resulting from the move to my new digs. I'll try and get some specific references unless someone knowledgeable can jump in here.....Doc
     
Thread Status:
Not open for further replies.

Share This Page