Does length matter?

Discussion in 'Technical Questions & Information' started by .308 shooter, May 23, 2012.

  1. .308 shooter

    .308 shooter Member

    May 3, 2008
    Sorry.... Bad joke.. I have an Ar build that's pretty accurate from the bench with a bipod and sandbags... 20" bushmaster heavy barrel (1:9 twist) w/ crowned muzzle, free floated Yankee Hill hand guard. I reload and get consistent 1/2" to 5/8" groups at 100yds with 69gr Sierra Matchking HPBT bullets. I also have a two stage Rock River Arms trigger... It's pretty nice.

    I'm looking at building a target upper for it. Thinking of a White Oak 26" 1:7" twist stainless barrel for it. Will the twist rate and extra 6" make that much difference in accuracy? I'm looking to get 1/4" to 3/8" groups or close. I know I'm doing pretty good as is, but want better out of an AR platform.

    Thanks in advance for your help.
  2. JLA

    JLA Well-Known Member

    Feb 26, 2007
    Heart Of Texas
    you will have to run heavier bullets to get the most out of it and they probably wont be short enough to run in a magazine. 7 twist at .223 velocity is ideal for 75-90 gr bullets

  3. LDBennett

    LDBennett Well-Known Member

    Dec 20, 2003
    Hesperia, CA
    The 7 inch twist makes heavy bullet mandatory. When you start using heavy bullet their length may preclude them fitting in the magazines and they become single feed cartridges (your might as well be using a bolt gun).

    My 7.5 inch twist Lothar Walthers barrel loves heavy bullets that still fit the magazine but it does not like normal 223 bullets like the 52 grain hunting bullets. The fast twist centrifugal force literally explodes the bullets before they even get to the target. It will kind of shoot 55 grain match or varmint bullets but not nearly as accurate as the heavier bullets up to 75 grains that fit the magazines.

    The twist and barrel length do not "make" a gun accurate. It is the quality of the barrel. Barrels made with precision (perhaps air tested and culled for accuracy or lapped and stress relieved) with tight chambers are part of the accuracy recipe. A good match grade barrel made by a reputable barrel maker with guaranteed accuracy performance goes a long way to match accuracy. My Lothar Walther barrel is a production match barrel and a custom match barrel from a quality match barrel manufacturer probably would out perform it. But the chambering is done by the gunsmith, not the barrel manufacturer typically, and can make or break the accuracy. Some barrel maker do offer custom chambering, though.

  4. cycloneman

    cycloneman Well-Known Member

    Dec 16, 2008
    I will throw in my 2 cents. I have an HK with a 1 in 7 bbl. It shoots 55 gr fmj all over the page. When i put in vmax bullets same weight i can put 10 rounds in a dime at 100 yrds.
  5. TRAP55

    TRAP55 Active Member

    Only on Muff guns.:D
    What JLA said about longer barrels with the heavier bullets.
    I had a 1-7 twist 24" that loved those 69grn BTHP Match bullets. I got the best results with powders that gave the highest velocity with the lowest chamber pressure in the longer barrel. 20x scope, on sandbags, and headshots on ground squirrels at 450yrds were consistent.
  6. JLA

    JLA Well-Known Member

    Feb 26, 2007
    Heart Of Texas
    LD is spot on with the accuracy explanation. Simply swapping for a new barrel with a faster twist will only change what bullets and powders will shoot well. If you really want to shrink your groups keep the set up you have and accurize it.

    Lap the barrel, and necksize the brass. Handweigh each and every powder charge for each and every round, segregate projectiles by weight at the very least, segregate your brass by weight at the very least. keep trim length consistent and uniform the flash holes. These are small tedious steps in the handloading process that can easily make your 3/4 MOA ammo into 1/2 or better.

    Keep in mind, your set up is already SUB MOA. That means somethins jivin'. All you need to do is fine tune your ammo and lap your bore for concentricity and consistency, as well as resistence to collect fouling. Clean well and clean often, like every 25 or 30 rounds often..
    Last edited: May 24, 2012
  7. jla is absolutley correct,refine what you have.i dont think starting over is the key.barrell length in itself is not going to improve acuracy,it only increases the distance from frount to rear sight.if you were shooting without a scope it could increase accuracy because of longer sight radius.i would go over your shooting procedure,trigger pull,rifle hold,follow thru. old semperfi
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