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Thread: 308 twist rate

  1. #1
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    308 twist rate

    Hi guys. Has anyone had any experience with a 1 in 7 twist .308 barrel? Probably 18 inches. Some subs but mostly 168gn and higher supersonic loads.
    Thanks in advance.

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  2. #2
    Member zarathustra's Avatar
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    Why 1 in 7"?
    I used to own an old Rem 788 with a Douglas 1:8 twist years ago...and that would be the fastest twist I would go. It was great with subsonics but found that it was very fusy when working up high velocity handloads. It didn't take much to hit high pressures of blown primers and that's the problem. With the larger diameter and heavier .308 bullets where it takes more force to go to full rpm in a high velocity load, you can reach too great a pressure just too easily in a tight twist barrel (in my experience)
    Guns don't kill...
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  3. #3
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    1 in 8 seems to be the standard rate for subs in 308. I'm sure a 1in 7 would still work. As above you'll find pressure a bit earlier, and i probably wouldn't be running 125's through it

  4. #4
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    you will also tear apart soft projectiles if you drive them at high velocity...the RPMs will just be too much for them....BUT flip side of that is that a projectile should open up well at less than full speeds.

  5. #5
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    Cheers everyone. Sounds like id be better off with a slower twist. Just had the option of a 1 in 7 to try.
    Thanks again.

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  6. #6
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    The standard .308 twist is 1:12" some match/Sniper barrels are 1:11" to handle 175 SMK's any faster twist is only for the real heavies like 230 grains
    if you only plan on using subs occasionly it would make sense to build it to handle the 150 to 180 grain bullets that are the standard for the .308
    subs only have a limited range no matter how streamlined they are they drop like rocks.
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  7. #7
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    for short barreled subsonics up to 1-5 work great
    1-5 seems to be the standard these days for the machined expanders and works just fine with supersonic
    the extra rotational energy is bugger all but it gets the expanders spinning like an outboard propellor inside the target giving you a bit more energy transfer
    you can go slower twist if your barrel is longer
    the fastest barrel I could get in NZ was a 1-8 trueflight at the time and I am very happy with it, I would prefer faster but this is a great barrel that shoots fantastically
    mine is 300blk just for subsonics

    this too fast twist thing isnt the issue that its made out to be from the research
    select your barrel up to stabilise the longest bullet you plan to run, but long story short 1-7 will be about as good as you can get and 1-8 will be a lot easier to find
    if you can import a barrel from x-caliber barrels in usa you can get the 1-5, and pacnor did 1-6 before they burnt down and are apparently nearly rebuilt so should be making barrels again soon

    I ask a lot of questions to Kevin brittingham from Q on instagram because they seem to be the cutting edge of subsonics with discrete ballistics
    its wort the watch to get your head around these things

    I used a 1-11 308 tikka t3 barrel full factory lenght for shooternz's 151gr cast bullets for ages before going fancy with 300blk
    to be honest it is basically exactly the same outcome with the same noise but now at least i get to carry something short and light

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  8. #8
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    I read your Initial message wrong, If its only some subs whatever barrel twist that is reccomended for the 168+ gr will do good enough for sub use

    1-7 or 1-8 would be great in your application 1-5 is pretty much just for short barrel subsonic dominant guns (which is my current obsession)

  9. #9
    Member zarathustra's Avatar
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    Quote Originally Posted by Bill999 View Post
    for short barreled subsonics up to 1-5 work great
    1-5 seems to be the standard these days for the machined expanders and works just fine with supersonic
    the extra rotational energy is bugger all but it gets the expanders spinning like an outboard propellor inside the target giving you a bit more energy transfer
    you can go slower twist if your barrel is longer

    1-7 or 1-8 would be great in your application 1-5 is pretty much just for short barrel subsonic dominant guns (which is my current obsession)
    Bill999 I just can't agree on your choice of 1:5" for sub and supersonic, and your statement that in a longer barrel you can use a slower twist rate.
    A twist rate of 1 in 5 means the bullet turns 1 full rotation per five inches of travel. A 1 in 8 twist means the bullet makes one revolution every eight inches of travel (it has to travel more distance to make a full rotation). But adding length to the barrel ie going from a 16" bbl to a 24" bbl will not make the bullet rotate faster than 1 time per 5 or 1 time per 8 inches of travel (whatever is the barrels twist rate).

    The only way a longer barrel could make the bullet rotate faster is that it has more internal space for powder to convert into expanding gas/pressure therefore velocity can increase. But that is mostly theoretical as one generally cannot reach safe pressures to increase the velocity enough to get RPM in a 1 in 8" twist longer barrel equal to a 1 in 5" shorter barrel.

    So to summarise: spin is dictated by the twist rate of the rifling, no matter the length of the barrel. 1 twist in 8" is the same from a 16 " barrel as it is from an 18", 20" or even 24" barrel... one complete rotation of the projectile every eight inches. Really the only practical variable that will affect RPM is the rate of twist... not barrel length.
    Guns don't kill...
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  10. #10
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    Im not sure what we dont agree on, most of what you are saying is spot on

    the bullet isnt getting rotated faster in the longer slower twist barrel(quite the opposite), it just has more time 'in barrel' to stabilise so has less issues
    have a look what the company that makes the "fix" by "Q" and the "Honeybadger" 300blk run 1-5 for sub/super use, and 1-7 or so for 308
    the typical barrel lenght is 5-7 inches for these guys for 300blk and 12-14" often for 308s
    its cool stuff

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    Greetings All,
    There has long been, in the US, a fear of projectiles being over stabilized resulting in poor accuracy. This may have had some basis years ago when projectiles were poorly balanced. Today almost all projectiles are of much better quality and fast twist has little if any effect. Still, however the myth persists. Twists in my .308 rifles run from 10 to 14 inch twists and generally shoot most projectiles well. One with a long throat does not shoot 150 grain boat tails well but shoots 150 grain flat base really well. I have not tried subs yet but will. Another .308 I am aware of with a 7 inch twist shoots everything well, including subs.
    Regards Grandpamac.
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  12. #12
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    Quote Originally Posted by grandpamac View Post
    Greetings All,
    There has long been, in the US, a fear of projectiles being over stabilized resulting in poor accuracy. This may have had some basis years ago when projectiles were poorly balanced. Today almost all projectiles are of much better quality and fast twist has little if any effect. Still, however the myth persists. Twists in my .308 rifles run from 10 to 14 inch twists and generally shoot most projectiles well. One with a long throat does not shoot 150 grain boat tails well but shoots 150 grain flat base really well. I have not tried subs yet but will. Another .308 I am aware of with a 7 inch twist shoots everything well, including subs.
    Regards Grandpamac.
    Allways appreciate your input @grandpamac . Cheers. I have committed to a 1 in 7 so looking forward to seeing how it shoots.

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  13. #13
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    Lowdown on twist rates affecting velocity -

    How Muzzle Velocity Changes with Different Barrel Twist Rates « Daily Bulletin

    Also a comment from another forum by Frank Green (co owner of Bartlein Barrels) -
    "Not only did we make all those barrels in the test but we chambered them as well. So same chamber reamer was used in all of them and the barrels where all made at the same time. If I recall correctly all of the barrels where made out of the same lot of material except for the left hand twist was out of a new lot. So about as identical as you can make them.

    It's always been my understanding that twist might have a small impact on velocity but for the most part it really doesn't in the grand scheme of things.
    "
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  14. #14
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    If you want to use cast bullets don't use a fast twist the slower the better my test rifle has a 1:13" twist and stabilises the 151HP down to 900 fps
    haven't tried to go lower not keen on a stuck bullet.
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  15. #15
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    I saw those videos regarding the q rifle and the 8.6 creedmoor ( more or less a 338 whisper or br which out the trade name ).
    Ask @Wingman what was the twist rate of his 338br and what projectiles he was shooting subsonic and how they where flying.
    For the majority of what we are doing , I don't think that super fast twist are of any use.
    Overstabilising at a rate of 1 in 5 twist might cause some failures in conventional cup and cord projectiles specially if flying at supersonic speed.

    When I started f class shooting in early 2000, I remember very well the competitors having the old 7mm a-max exploding in mid air when launched from a 1 in 8 twist with a fast 284 win or a magnum. Not all of them but 1 or 2 out of a series of 12 or 15 was enough to make it to the bottom of the scoring board.

    The 6mm ppc and 30 br and their wildcat cousins still win matches with 1 in 14 and 1 in 17 twist respectively.

    Why is the venerable 22 lr still flying so well in 1 in 16" twist?

 

 

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