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Thread: Why not 1/8 twist?

  1. #31
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    Quote Originally Posted by mastiffhound View Post
    Would a 1 in 8 improve my groups? Who knows, every barrel is different it seems to me. I don't feel the need to try one out when I finally use up my current barrels either, 1 in 7 has been more than sufficient for my needs. A 1 in 9 might be more appropriate for 55gr loads I usually shoot but I sometimes use 69 and 77gr Nosler custom comps and they shoot very well in both my 1 in 7 barrels. Do you have a reason to go for a 1 in 8 twist? I think that's a better question than why not.
    I would hope nobody would waste the money on switching out their current 1/7's for 1/8's. It's just not worth it in my opinion. If you're looking to buy a new barrel though, I wouldn't choose it based on whether or not it's 1/7 or 1/8. In my personal opinion, there are other factors more important. If you're going after a hammer forged barrel then it's most likely going to be 1/7 but if you're looking for a Stainless barrel, it's most likely going to be 1/8.

    That being said, twist rates just can't be disregarded. There isn't a magic twist rate that will shoot every weight as accurate as they can be. A think people tend to make it more dramatic than it really is though. Most people are going to be shooting inside and at 100 yards and at this distance, a 1/7 barrel is not going to throw a 40gr pill off the paper. I've never seen it happen and I've never heard of it happening. What can happen though is overstabilization and it will open up your groups. Going back to what I said before. The average shooter won't see it because they aren't shooting at distances where it's going to be apparent.

    A little history I believe is accurate: When the M16-A2 was put in service, that's when the 1/7 twist was introduced. Not because it stabilized the 62gr green tips better but because it was needed so the longer tracer rounds could hold on to enough phosphorus to burn past the military requirement of 900 meters.


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    Last edited by Obscenejesster; 02-16-14 at 00:49.

  2. #32
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    M855 and M856 was the new ammo that was developed for the M249. The 1:7 twist was used for the M249 in order to stabilize the longer M856. It is only 1.7 grains heavier, but is 6.3mm longer.
    As they were going for ammo compatibility, the new M16A2 came with the same barrel twist.

    Twist rates are important though. Shooting a heavy/long bullet from a slow twist barrel can cause it to lose static stability, and it will start to tumble. Shooting a light weight bullet through a fast twist barrel can cause overstabilization, which results in the projectile flying nose high, and landing base down. This can cause accuracy issues at longer ranges, as the projectile loses velocity faster and will be more prone to drift.
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  3. #33
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    Quote Originally Posted by Obscenejesster View Post
    The lightest the Mil goes is 55gr....right? I think 1/7 is good for them but I believe the average civilian would benefit more from 1/8. There are some very nasty rounds that come in less than 55gr and 1/7 can be just a little to fast for them.

    Not to mention, I think 1/8 is probably the best SHTF twist you can get. It should be dead accurate with any round you come across. Then again, a few inches here or there probably wouldn't matter when the zombies get here.

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    What rounds might those be? Unless you are talking about very nasty rounds against varmints that is. The 1/7 is perfectly fine for 55gr or 50gr TSX bullets which are the lightest I would go for any defensive round. On the other hand 1/8 is barely adequate to stabilize the 70gr TSX which is probably one of the most terminally effective bullets on the market.

    If you want to talk accuracy, the quality of the barrel will make far more of a difference than twist rate.
    Last edited by vicious_cb; 02-16-14 at 03:42.

  4. #34
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    Technonlogy and warfare change. A light as shit m16a1 (and m193) was a good jungle weapon I'm sure. I also know that a very significant number of Short barreled colt xm177 were used by SOF in vietnam. Going off of what I know about Vietnam from relatives who served multiple tours in group and light infantry units, almost all engagements were under 100 meters compared to Afghanistan were 900 meter firefights can be common. Plus I believe popular doctrine of the day was to react to close ambush by hip firing on full auto. Suppression is one thing shooting blindly is another. There is a reason we do not hip fire anymore including when in a close ambush.

    I know in Iraq I had to engage targets house to house and room to room. IN RC west I have literly been in firefights at 1 km. Talk about apple and orange enagment distances. Now a m4 is almost useless as a point target weapon at 900 meters but those engaments were usually MG duals with almost useless airbursting RPGS used by the Taliban and effective sniping by us. Then two hours latter I could be in a mud village possibly engaging targets 10 or 20 meters away. I think the army made the right call by going to the m4 as a fit all weapon. I never felt unadequately armed with a m4/m855 combo.
    Last edited by ST911; 02-16-14 at 10:08. Reason: Thread clean up

  5. #35
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    Quote Originally Posted by vicious_cb View Post
    What rounds might those be? Unless you are talking about very nasty rounds against varmints that is. The 1/7 is perfectly fine for 55gr or 50gr TSX bullets which are the lightest I would go for any defensive round. On the other hand 1/8 is barely adequate to stabilize the 70gr TSX which is probably one of the most terminally effective bullets on the market.

    If you want to talk accuracy, the quality of the barrel will make far more of a difference than twist rate.
    Yup, interms of barrel quality being far more important than twist rate, that's what I said a couple posts up.

    Getting onto the fact you think 1/8 twist can barely stabilize a 70gr pill. I have nothing else to say except that this information is false and nobody should be listening to it.

    I've never come across a 1/8 barrel that can't stabilize a 77gr pill let alone one that weighs 70gr. In fact, I'm looking at a box of 77gr Sierra Match Kings and right on the box, it says "1/7 or 1/8 twist only". Most of the precision guys are using 1/8 barrels and shooting either 77gr Sierra's or 77gr Noslers.

    If you look around, you will actually find, most match and SS barrels are only offered in 1/8 twist.

    Maybe you got confused and instead of typing 1/9 you types 1/8. If you didn't get confused then please stop spreading false information. Bottom line....1/8 is plenty fast to stabilize 77gr pills. Hell, some 1/9 barrels can stabilize a 77gr pill.

  6. #36
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    One of the big points that sold me on a Microtech STG-556 was the 1/8 twist barrel. I think it's perfect.

  7. #37
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    I am a fan of 1/8 twist barrels as they kind of remind me of an SUV. Master of nothing, but good all around.


    For me, I use the BCM 410SS barrel for my long range shooting (varmint, paper, etc). It is in 1/8 and shoots Hornady 55gr Varmint Express awesome and shoots 77gr MK's very well too.




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  8. #38
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    But what if you need to shoot tracers in Siberian winters? How will you ever get them to stabilize in a 1:8?

  9. #39
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    Quote Originally Posted by BSmith View Post
    But what if you need to shoot tracers in Siberian winters? How will you ever get them to stabilize in a 1:8?


  10. #40
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    Quote Originally Posted by Obscenejesster View Post
    ...Getting onto the fact you think 1/8 twist can barely stabilize a 70gr pill. I have nothing else to say except that this information is false and nobody should be listening to it...
    Bullet length and shape is more important to determining what RPM is needed to stabilize the bullet in flight than it's weight. The TSX is a solid copper bullet and is longer than a lead core bullet of the same weight.

    Sierra uses doppler radar to measure the ballistic coefficient of bullets in flight. They have found the more stable the bullet, the less drag it has because it has less precession. The Sierra 69 gr Matchking (which is shorter than the 70 gr TSX), was found to have a better BC when fired from a 1:7 twist barrel than anything slower, including the 1:8.

    The biggest problem with faster RPMs is that it's hard on lightly constructed bullets. In the late 60s, my father bought a 22-250 and developed a firewalled load using the Hornady 50 gr bullet, one designed to give explosive terminal performance on small critters at 223 velocities, that pushed it close to 4000 fps. We called it the Blue Streak Express because whenever he fired it, the bullet would leave a faint trail of blue smoke behind it. Turns out Dad was driving that bullet to the point it was on the verge of self destructing from the centrifugal forces. Twist on that rifle was 1:12.

    Today's 22 caliber bullets are made to withstand being shot from the ever popular 22-250 and there is little danger of them coming apart when fired at the reduced velocities of the 223/5.56 even with their tighter twist.

    There are more and more reports from serious shooters showing a trend that the 1:7 twist does indeed have an edge accuracy over the 1:8 at longer ranges
    Last edited by MistWolf; 02-16-14 at 12:33.
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