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Thread: Barrel twist

  1. #1
    Boolit Mold
    Join Date
    May 2020
    Posts
    26

    Barrel twist

    I've got a lot of experience loading jacketed bullets in .308, .30-06, 6mm and 7mm. The world of cast boolits is both weird and wonderful. There's enough learning here to keep me busy for the next few decades, for sure. I've been trying to figure out an acceptable twist rate for a .308. Is there a dumbed down formula that doesn't require me to drag out Dad's slide rule? I believe my Remington 700 Varmint has a 1 in 12 twist and I'm hoping that ought to be good enough.

  2. #2
    Boolit Grand Master

    Join Date
    Mar 2013
    Location
    Northwest Ohio
    Posts
    12,383
    On my NM service rifles for 200-1000 yds I used 1-10 twist barrels shooting 168 grn - 175 grn BTHP bullets. Krieger made them in 1-10 1-12 and for those who couldnt decide 1 11.

    There are calculators on lone that do a good job of giving the twist rate for a given length of bullet at a given velocity. The need Twist is determined by velocity dia and length of bullet not weight

    To give an example, My 223s with 1-7 twist will stabilize an 80 JLK VLD at 2750 fps out past 600 yds My ar 10 in 22-250 with 1-7 twist will almost stabilize a 90 grn JLK VLD at 3400 fps the only difference is the velocity.

  3. #3
    Boolit Grand Master


    Larry Gibson's Avatar
    Join Date
    Jul 2005
    Location
    Lake Havasu City, Arizona
    Posts
    18,722
    "I've been trying to figure out an acceptable twist rate for a .308."

    Depends on how fast and how accurate at what maximum range you want to shoot cast bullets out of your .308W. Your 12" twist barrel with a proper cast bullet of proper alloy (ternary), sized, lubed and loaded correctly can get you upwards of 2300 - 2400 fps with sub 2 moa accuracy out 500 and maybe 600 yards. It should be "good enough" but a lot of that depends on you......"garbage in, garbage out"....Quality in casting and loading is paramount. BTW; my CBA match commercial rifle is a M70 target rifle with a 26" factory barrel chambered in .308W with a 12" twist.

    On the extreme side here is an 11 shot group just under moa (about 5.9") at 600 yards shot out of a 30x60 XCB rifle with a 16" twist barrel. The bullet was the NOE 310-165-FN "30 XCB" running at 2900+ fps.

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    For best accuracy you'll want to keep the RPM [fps x 720/twist in inches] at or below 140,000.
    Larry Gibson

    “Deficient observation is merely a form of ignorance and responsible for the many morbid notions and foolish ideas prevailing.”
    ― Nikola Tesla

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Abbreviations used in Reloading

BP Bronze Point IMR Improved Military Rifle PTD Pointed
BR Bench Rest M Magnum RN Round Nose
BT Boat Tail PL Power-Lokt SP Soft Point
C Compressed Charge PR Primer SPCL Soft Point "Core-Lokt"
HP Hollow Point PSPCL Pointed Soft Point "Core Lokt" C.O.L. Cartridge Overall Length
PSP Pointed Soft Point Spz Spitzer Point SBT Spitzer Boat Tail
LRN Lead Round Nose LWC Lead Wad Cutter LSWC Lead Semi Wad Cutter
GC Gas Check