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tbd1966
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Posted: 10/9/2008 6:07:33 PM
Can someone break down the wight to twist details?

I'm sure there is a post in here already addressing it so linking that would be great too.

So many manufacturers are providing 1 in 7 and 1 in 9 with some offering 1 in 10. Whats the main difference? Is there one that allows you to be accurate with all bullet weights, 55, 62, 68 etc. If not then whats best?
macgyverpwnage
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Posted: 10/9/2008 6:14:13 PM
[Last Edit: 10/9/2008 6:17:52 PM by macgyverpwnage]
From what i understand, 1 in 9 is for your standard 55gr M193 and 62gr M855 ammunition, maybe slightly heavier. 1 in 7 will stabilize 55gr and 62gr, but not as well as 1 in 9. However, 1 in 7 will allow the use of heavier 75gr and 77gr ammunition. 1 in 9 struggles with this heavier ammunition. I don't know much about 1 in 8 but I'm pretty sure its the median, being able to stabilize 55gr and 77gr alright, but bullets in the the middle of those two are the best for it. I'm not sure about 1 in 8 though. Anything higher than 1x9 is usually in bolt action rifles as far as I can see. They are for lighter bullets.

Edit: My rifle is a basic varmint/pest annihilator and self defense rifle, so I got a 1 in 9. That's all Del-ton has in their midlength kit. The barrel on my M16A2 is 1 in 7 twist.
Wideglide
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Posted: 10/10/2008 5:05:36 PM
As of a test yesterday, I can gaurantee that 1 in 9 won't shoot 80 grain match bullets.I had a few and shot them to see if by chance they would stabilize and they will not.




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BumpFireNHaveMoreFun
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Posted: 10/11/2008 12:06:42 AM

Originally Posted By macgyverpwnage:
From what i understand, 1 in 9 is for your standard 55gr M193 and 62gr M855 ammunition, maybe slightly heavier. 1 in 7 will stabilize 55gr and 62gr, but not as well as 1 in 9. However, 1 in 7 will allow the use of heavier 75gr and 77gr ammunition. 1 in 9 struggles with this heavier ammunition. I don't know much about 1 in 8 but I'm pretty sure its the median, being able to stabilize 55gr and 77gr alright, but bullets in the the middle of those two are the best for it. I'm not sure about 1 in 8 though. Anything higher than 1x9 is usually in bolt action rifles as far as I can see. They are for lighter bullets.

Edit: My rifle is a basic varmint/pest annihilator and self defense rifle, so I got a 1 in 9. That's all Del-ton has in their midlength kit. The barrel on my M16A2 is 1 in 7 twist.


So your saying in a 1:7 barrel lighter ammo will have less stability / accuaracy at longer ranges than a 1:9?
Hebrew_Battle_Rifle
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Posted: 10/11/2008 1:06:20 AM
[Last Edit: 10/11/2008 1:07:49 AM by Hebrew_Battle_Rifle]
The weight is of no concern in regard to twist rate. It is the length that matters. The longer the bullet, the faster the twist rate must be to stabilize it.


A 162 gr 30 cal A P bullet will need a faster twist rate to stabilze than a 165 gr copper jacket lead core bullet. The A P( Armor Piercing) bullet is longer and therefore needs a faster rate than the heavier 165 gr.
HotLead
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Posted: 10/11/2008 10:20:22 AM

Originally Posted By Hebrew_Battle_Rifle:
The weight is of no concern in regard to twist rate. It is the length that matters. The longer the bullet, the faster the twist rate must be to stabilize it.


A 162 gr 30 cal A P bullet will need a faster twist rate to stabilze than a 165 gr copper jacket lead core bullet. The A P( Armor Piercing) bullet is longer and therefore needs a faster rate than the heavier 165 gr.


I concur; the 1:7 twist rate was chosen out of necessity in order to stabilize the longer 64gr M856 tracer projectiles in use by the military. Rifling twist rate can be determined for a bullet of a given size, by using the Greenhill formula, which determines twist based on length-to-diameter ratio.

-JD
jason_h
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Posted: 10/11/2008 3:30:36 PM

Originally Posted By BumpFireNHaveMoreFun:

Originally Posted By macgyverpwnage:
From what i understand, 1 in 9 is for your standard 55gr M193 and 62gr M855 ammunition, maybe slightly heavier. 1 in 7 will stabilize 55gr and 62gr, but not as well as 1 in 9. However, 1 in 7 will allow the use of heavier 75gr and 77gr ammunition. 1 in 9 struggles with this heavier ammunition. I don't know much about 1 in 8 but I'm pretty sure its the median, being able to stabilize 55gr and 77gr alright, but bullets in the the middle of those two are the best for it. I'm not sure about 1 in 8 though. Anything higher than 1x9 is usually in bolt action rifles as far as I can see. They are for lighter bullets.

Edit: My rifle is a basic varmint/pest annihilator and self defense rifle, so I got a 1 in 9. That's all Del-ton has in their midlength kit. The barrel on my M16A2 is 1 in 7 twist.


So your saying in a 1:7 barrel lighter ammo will have less stability / accuaracy at longer ranges than a 1:9?


Light bullets will be "over-stabilized" in fast twist barrels, such that at longer ranges the axis that the bullet spins about will stay constant in orientation instead of shifting and staying in line with with the trajectory of the bullet. This isn't an issue at 100-200 yds, but as you get out to +600 yds, accuracy will probably start to suffer.

jst_71
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Posted: 10/16/2008 12:51:37 PM
Hello all... I'm new to the forum.
I found it while researching info about AK's.
Ended up returning the one I had purchased due to a problem and am thinking of going with a Del-Ton DTI. My only beef with the M4 is the shorter hand guard. I started looking at the seperate uppers on AIM and then noticed the difference in twist.

I had forgotten all about that! SO... I came back here to start researching.

After reading all these posts I'm still confused. I understand the tighter twist to stabilize heavier / longer rounds, but am fuzzy if you're stuck using a specific grain in either a 1x9 or a 1x7?

Will it matter which twist you go with if you're not looking for long range shots?

Thanks!
jst_71
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Posted: 10/16/2008 12:54:33 PM
height=8


I think mine is a minority opinion, but one can argue that 1/9 is better than 1/7 for most people, most uses, most of the time. It is an all-round general purpose barrel twist. And for most shooters its not going to matter with 55 gr ammo.

In the unlikely event TEOTWAWKI happens, and a friendly GI gives you a free magazine of 77gr, the 1/9 barrel will do just fine.

But its a hobby - get what you want. If it is important to you to shoot the current GI rifle, then get 1/7. If you are into precision rifle shooting, 1/8 or 1/12 may be best, depending on bullet weight. If you are going to plink at tin cans and 100 yard paper targets (like I do) with off the shelf ammo, then 1/9 is just fine (if not better).


I should have kept reading onto the next topic before asking! I think this answers my question!
QuinlanV
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Posted: 10/16/2008 1:54:03 PM
GaShoot4defense
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Posted: 10/16/2008 2:02:34 PM
nice chart but how to you tell how long a bullet is when you buy commercial ammo, does it say somewhere on the box??
meyekal
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Posted: 10/16/2008 2:43:31 PM

As a new member to the boards, I would reccomend reading the ammo oracle document under the Amunition forum faq. It explains this topic very well, and is worth the read