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Thread: Which twist rate for the 6BR Norma?

  1. #1
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    Which twist rate for the 6BR Norma?

    I have made up my mind to pursue building a 6BR Norma rifle for 100 yd 300 yd informal bench shooting. The next step is to determine the appropriate rate of twist and what I plan to shoot.

    Based on what I have read and advice I have received, Im thinking a 12 twist barrel for shooting 60gr 80gr bullets at these shorter distances.

    I haven't checked all sources yet but it looks like a 12 twist barrel is probably going to require a long lead time order. On the other hand, 8 twist barrels are in stock and available.

    Is the 8 twist versatile enough to shoot the lighter bullets at short range or would you recommend that I hold out for the slower twist?

  2. #2
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    If your just going to shoot the 60-80gr bullets then stick with the 12 twist.

    The 8 twist if you get a lower quality batch of bullets or should I say your ammo/bullets have any runout etc...the faster twist will amplify the wobble of the bullet. Think of it this way...any runout your ammo has when the bullet makes the jump to the rifling it already has an alignment issue/premature wobble to it. The faster twist will amplify the wobble and have a negative effect on the accuracy.

    Shooting the lighter weight bullets you don’t want 5R style rifling. Stay with conventional/standard rifling. Standard 4 groove, standard 5 groove etc...

    Later, Frank
    Bartlein Barrels

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    I guess the other question that should be asked is....

    What is your accuracy requirement?

    The 105-110gr bullets are going to cut the wind better if it’s windy out.

    I rebuilt an older Savage 112V from the 70’s. The new barrel is a 7 twist (I have no intentions of shooting bullets lighter then 105gr.) and with 5R rifling and chambered in 6BRA. The rifle easily shoots in the .2xx’s at 117 yards (shortest target I have at home). I’ve only shot it out to 430 yards and it will do anything that I want it to do. If my son or wife wants to go to a F class match is a easy shooting gun that they can use for any distance.

    Good working everyday loads with 110gr ATIPs are coming out at 2822fps (barrel is 26”) and 107SMK are coming out at 2882fps.

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    Quote Originally Posted by Shortbox4x4 View Post
    I guess the other question that should be asked is....

    What is your accuracy requirement?

    The 105-110gr bullets are going to cut the wind better if it’s windy out.

    I rebuilt an older Savage 112V from the 70’s. The new barrel is a 7 twist (I have no intentions of shooting bullets lighter then 105gr.) and with 5R rifling and chambered in 6BRA. The rifle easily shoots in the .2xx’s at 117 yards (shortest target I have at home). I’ve only shot it out to 430 yards and it will do anything that I want it to do. If my son or wife wants to go to a F class match is a easy shooting gun that they can use for any distance.

    Good working everyday loads with 110gr ATIPs are coming out at 2822fps (barrel is 26”) and 107SMK are coming out at 2882fps.
    Am I misleading myself by interpreting that the heavier bullets won't perform as well as lighter bullets at shorter ranges? If so, that make the decision a little easier.

  5. #5
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    Also you can run the faster twist like a 1-8 etc...You can still shoot a flat base bullet. You might give up a little bc but you might find them easier to tune. BIB’s bullets are very good/popular. Also Bart’s Bullets are very nice as well.

    It’s what.....what is the accuracy you want out of the gun question you have to ask yourself. If the rifle shooting in the .3xx’s or a tad better is good enough for you then the fast twist barrel is where I would go and shoot the heavier bullets.

    What most people don’t realize is (this applies to most match bullets) that in the real world the bullet at best can only give them 1/3moa to maybe a 1/4moa. You want bullets capable of 1/4 consistently or even better than your going full custom or making your own. That’s why the bulk of the top short range BR shooters are making they’re own bullets. A gun that shoots low .2xx’s isn’t necessarily good enough for them.

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    Here are a couple pictures of groups. The first one is a 10 shot group with one load. The other one is a 5 shot group with a different load (first time out with a new powder so first round of testing on that one).

    Again this is not a bench rifle per say but a varmint style rifle that can do double duty as a f type gun. It has a factory stock and not flat bottom type benchrest stock.
    Attached Thumbnails Attached Thumbnails 20190728_185441.jpg   1573442414486.jpg  

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    "On the other hand, 8 twist barrels are in stock and available"
    So, what does that tell you?
    Go 8 twist, ZERO freebore, no turn neck.

    Start off with the lightest bullets you can get your hands on, probably 45 or 50 grain, stuffed at or into the lands and go heavier as the throat wears, and it will. Probably faster than you might like.
    Make sure you bring another rifle to shoot when you shoot the 6 BR. Bug hole accuracy gets BORING real fast.
    Oz never gave nothing to the Tin Man, that he didn't already have.

  8. #8
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    Quote Originally Posted by Nor Cal Mikie View Post
    "On the other hand, 8 twist barrels are in stock and available"
    So, what does that tell you?
    That's a good point.

  9. #9
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    A good rule of thumb is to buy only as much twist as absolutely necessary to stabilize your intended bullet. A 12 twist will eliminate using heavier bullets. An 8 twist will shoot both, but with slightly less accuracy or consistency with lighter bullets, as long as you don't have wind to worry about.

    FWIW I built a 6mmBR with 28 inch Criterion bull barrel in 8 twist on a Savage 12FV action and it shoots tiny groups using 107SMK's, but then I don't compete with it. If you're just hobby shooting like me, ultimate accuracy is not as big a draw as when you're spending lots of coin to compete. JMOP.

    My advice: get a big, long, fat barrel, load it with 105 to 108 grs bullets and shoot the snot out of it.
    Long distance shooters are a different breed, and I would never want to piss off someone who can "pick you off" from another zip code.

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