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Posted: 10/10/2002 6:14:46 PM EDT
I know what these ratios mean, as in rate of twist in the barrel. What I'm not sure about is what kinda difference does it make in practical terms? Thanks.
Link Posted: 10/10/2002 6:48:43 PM EDT
http://www.ecis.com/~mraudio/AR15_Ammo_FAQ.htm
Link Posted: 10/10/2002 6:50:13 PM EDT
Im no expert will try to help. 1/7 will stabalize heavier bullets. Some say that long range shooting 55 grain out of one isnt that accurate. But praboly for 100 yards will be fine. Mine is anyhow.The 1/12 is really good for the 55 grain. the 1/9 and 1/8 is a inbetween. Best of
both worlds. The military uses the 1/7 in the M16A2's. Iwas told it was to stabalize the tracer round. The Vietnam M16 used the 1/12 ( I think ).I have the 1/7 in a colt and a 1/9 in a Bushmaster. Hope Ive helped , War Dawg
Link Posted: 10/10/2002 6:52:04 PM EDT
http://www.ammo-oracle.com

Extensively covered, well-developed, massively-gathered amount of information here.
Link Posted: 10/10/2002 6:54:06 PM EDT
[Last Edit: 10/10/2002 6:55:55 PM EDT by Dano523]
They refer to the distance that the bullet travels down the barrel and twists.

Hence a 1/12 means the bullet twists 1 time in 12".

The twist is relevant to bullet weight. A 55gr rounds best performance is achieved with the 1/9, the 62gr with 1/8 and so one. If the bullet spins does not spin enough, then the bullet starts to destabilize, if too much, then the bullet struggles down range(not sleeping) and the group opens up.

Hope this helps.
Link Posted: 10/10/2002 7:09:43 PM EDT

Originally Posted By MaverickMkii:
www.ammo-oracle.com

Extensively covered, well-developed, massively-gathered amount of information here.

Link Posted: 10/11/2002 6:36:59 AM EDT

Originally Posted By Dano523:

A 55gr rounds best performance is achieved with the 1/9, the 62gr with 1/8 and so one.



Actually, per "The Black Rifle", chart p. 341 (Courtesy Fabrique Nationale Herstal)

1/12 handles the 55 gr. M193 most accurately,

1/7 handles the 62 gr. SS109, i. e., M855 most accurately, and

1/9 handles both well, but is slightly less accurate than either of the above.

No mention is made of 1/8.
Link Posted: 10/11/2002 12:19:40 PM EDT
Link Posted: 10/11/2002 12:46:10 PM EDT
Troy, although the FAQ is very good, I don't think either "The Black Rifle", the chart on p. 341, or Fabrique Nationale Herstal, are putting out crap.

I leave it for the readers to decide for themselves (take a look at the chart.)
Link Posted: 10/11/2002 1:05:21 PM EDT
[Last Edit: 10/11/2002 1:06:49 PM EDT by eswanson]
Well, without having access to a copy of "The Black Rifle", page 341, it's hard to look it up, but the generalizations quoted above are crap. Especially in light of the fact that a 1/9 twist will stabilize and give perfectly good accuracy on bullet weights up to 75 grains, and on a good day, 77 grains. I shoot 69gr Sierras out of mine all the time with wonderful accuracy.
Link Posted: 10/11/2002 1:13:23 PM EDT
es, no one said 1/9 wouldn't do every bit of what you said, only that it was slightly less accurate with M855 than 1/7, and slightly less accurate with M193 than 1/12.

Now, I might add, which twist is the compromise, then?
Link Posted: 10/11/2002 3:35:36 PM EDT
SanchoPanza,

Quoting from books is fine, if your looking for a general answer. My self, I posted what I have found by testing barrels and loads.

I would suggest that before you bash a post, you do a little testing to come out with your own findings. Spewing information from just book sources will get you into trouble every time.

P.S. My tests for the last few years have been at 4000' elevation, and both in hot wether and cold wether. All of the my rounds for testing have been hand loads worked to find the barrel/rifles sweet spot.

Have a nice day.
Link Posted: 10/11/2002 4:48:19 PM EDT
Well, I am certainly no expert in bench rest shooting, but in my experience playing around with AR's in a multitude of calibers.....it sure seems that the best groups are usually turned in by barrels leaning on the slow side of the twist window. Running a twist that is just fast enough to keep the bullet stabalized seems to be the answer for me. Tightening up the twist seems to give you a broader window of "acceptableness" but is not optimum.

If you want every bullet weight to work, I would tighten up the twist, but if have the option to narrow up the window for a particular bullet, I would lean it out. Just my experience.....no real knowledge speaking here.

Tony Rumore
Tromix Corp
Link Posted: 10/11/2002 6:03:05 PM EDT

There is a 'sweet' spot for max accuracy re bullet weight and twist:

1:12 - 55grn
1:9 - 62grn
1:7 - 69grn

1:9 is the best compromise barrel twist for most of us though hard-core target shooters will go with 1:7.

(The info in the "Black Rifle" is not quite accurate.)
Link Posted: 10/11/2002 8:02:04 PM EDT
Please remember that the WEIGHT of the bullet is not what is important but the LENGHT of the bullet that matters. The LONGER the bullet the TIGHTER the twist needed to stabilize it. The DENSER the medium the FASTER the twist.

So the military started out with 1/14" for the M16. But in COLD air which has a greater DENSITY the bullet was not stable. They tightened the twist to 1/12" to stablize that LENGTH of bullet in all air DENSITIES we find on earth. Then they designed a longer 62 grain round. It required a twist of 1/9" to stabilize it. However the tracer rounds had a less dense material in them and were LONGER even though it was similar in weight. So the twist needed to be 1/7" to stablize the LONGER bullet. Heavy match bullets are LONG and require fast rates of twist to be stable. The heavier bullet the tighter the optimal twist will be if similar construction is used. To fire a 55 grain steel bullet would require a faster than 1/12" twist because the steel is not dense and the bullet would have to be LONGER than a lead 55 grain bullet.

If a bullet travels though VERY DENSE materials like water or body tissues it will become unstable and try to do what is natural and travel heavy end first. Thus they yawing you get with most rifle bullets. This is also why pistols that can be fired under water but are designed for shooting through the air become unstable after a short distance and the bullets veer off in a random direction.

I hope this explains twists and gyroscopic stability for you
Link Posted: 10/14/2002 10:49:07 AM EDT
[Last Edit: 10/14/2002 10:56:47 AM EDT by SanchoPanza]

Originally Posted By Dano523:
SanchoPanza,

Quoting from books is fine, if your looking for a general answer. My self, I posted what I have found by testing barrels and loads.

I would suggest that before you bash a post, you do a little testing to come out with your own findings. Spewing information from just book sources will get you into trouble every time.

P.S. My tests for the last few years have been at 4000' elevation, and both in hot wether and cold wether. All of the my rounds for testing have been hand loads worked to find the barrel/rifles sweet spot.

Have a nice day.



Dano523, respectfully suggest you read a little more. My post refers ONLY to M193 & SS109 (M855) [obviously not a RELOAD, so we could both be correct.]

However, your GENERAL & DOGMATIC post left off a few vital facts, so, NOW you tell me...

Have a nice day.
Link Posted: 10/14/2002 10:52:44 AM EDT
Btw, for those who state that the info in "The Black Rifle" is not accurate, well, it's a shame none of you have the credibility that FN has.

But, since you don't, proof will be required, not blanket statements, or un-footnoted references.

I've cited my source. Please cite yours.
Link Posted: 10/14/2002 11:20:52 AM EDT
Link Posted: 10/14/2002 11:45:50 AM EDT
You know, Troy, I don't see it that way. But, I do not see the burden of proof on me, but rather the other way around. You can't dispove this info simply by repeating yourself.

I have posted a credible source (FN) while others, doubtless proponents of the 1/9, have NOT.

Of course, you can choose to believe what you will.
Link Posted: 10/14/2002 12:59:02 PM EDT

Originally Posted By SanchoPanza:
You know, Troy, I don't see it that way. But, I do not see the burden of proof on me, but rather the other way around. You can't dispove this info simply by repeating yourself.

I have posted a credible source (FN) while others, doubtless proponents of the 1/9, have NOT.

Of course, you can choose to believe what you will.



You're from Cuba? WTF?
Link Posted: 10/14/2002 2:01:54 PM EDT
LoL, no just hope to retire there one day.
Link Posted: 10/14/2002 3:18:28 PM EDT
[Last Edit: 10/14/2002 3:19:22 PM EDT by 5subslr5]

Originally Posted By SanchoPanza:



Actually, per "The Black Rifle", chart p. 341 (Courtesy Fabrique Nationale Herstal)

1/12 handles the 55 gr. M193 most accurately,

1/7 handles the 62 gr. SS109, i. e., M855 most accurately, and

1/9 handles both well, but is slightly less accurate than either of the above.

No mention is made of 1/8.
----------------------------------------------

I understand why the 1:12, 1:9 and 1:7 and even the very early 1:14 but don't have a clue as to why a 1:8.
Anyone have a clue ?????
Link Posted: 10/14/2002 7:10:40 PM EDT
I don't want to wade into a flame war here, but figured I'd throw my two cents in anyway.

Me and a friend of mine recently did a test with three different rifles (Bushmaster Gov Profile 1/9, Colt Match HBAR 1/7, Colt Gov Profile 1/7), and with Federal Lake City M193, and Spanish SS109.

All shots were shot slow fire from the prone at 100 yards.

All the rifles were more accurate with the SS109, but all all the rifles held consistant groups. All within about a half inch.

After hearing all I had heard about the 1/7 VS. 1/9 debate (specificly when it comes to the 55 gr M193 and the 62 gr SS109) that I'd see a noticable decrease in accuracy with 55 gr ammo in the 1/7 at 100 yards. But I didn't. All the variances were within a half an inch. Not enough to convince me at this point that the M193 is significantly less accurate out of the 1/7. I could see however that it may be much more accurate out of the 1/12.

Now of course, with a good scope and sandbagged, the inaccuracy might show up a little more (or or that matter at 300 yards). But at 100 yards with irons? I'm pretty comforable with M193 with either 1/7 or 1/9.

Link Posted: 10/15/2002 5:33:35 AM EDT
It's a pretty close run thing, even if you use the FN chart.

No doubt each individual barrel will vary, and each shooter. Kind of a "your mileage may vary" disclaimer.
Link Posted: 10/15/2002 6:06:49 AM EDT
Heck, and where do I stand with my 1:10 barrel. What are my "ideal" bullets ? 55gr ? 62gr ?

C-2-6
Link Posted: 10/15/2002 6:29:13 AM EDT

Originally Posted By Charlie-2-6:
Heck, and where do I stand with my 1:10 barrel. What are my "ideal" bullets ? 55gr ? 62gr ?

C-2-6



Charlie, for all practical purposes I would think what's correct for the 1:9 should be fine for your 1:10. (At least technically, the 62 grn should be modestly more accurate.)
Link Posted: 10/15/2002 1:02:11 PM EDT
Link Posted: 10/15/2002 1:29:02 PM EDT
HA! Who says your not just a gifted webmaster who created those sites just to support your theory? Hmmm?

(I have a 1-13 Kreiger. Made for lil' bullets. Been playing with 52 Matchkings. After I get the .458 maybe I'll get a normal barrel.)
Link Posted: 10/15/2002 1:57:27 PM EDT
<sigh>

Only the Bushmaster FAQ speaks directly to the issue at hand.

"The 1 in 7" barrel was a military development created to stabilize a long tracer round"

This is an error of sorts, per "The Black Rifle", p. 340, "the SS109, especially it super-long tracer version the L110 (fig. 363), required a faster rifling twist (FN recommended 1 turn in 7 inches) in order to stabilize."

i. e. it wasn't only to stabilize the tracer round.

"the 1 in 9" chrome lined is the best and longest lasting compromise we have found"

Even Bushmaster calls 1/9 a "compromise".

Would be nice to get our hands on the: Fabrique Nationale Herstal, Belgium Improved Ammunition 5,56x45. FN Report No. TW7, dated October, 1980 (cited in The Black Rifle Bibliography, p. 397).
Link Posted: 10/15/2002 4:25:12 PM EDT
[Last Edit: 10/15/2002 4:25:53 PM EDT by Troy]
Link Posted: 10/15/2002 4:32:32 PM EDT

Originally Posted By SanchoPanza:
<sigh>
Only the Bushmaster FAQ speaks directly to the issue at hand.

"The 1 in 7" barrel was a military development created to stabilize a long tracer round"

This is an error of sorts, per "The Black Rifle", p. 340, "the SS109, especially it super-long tracer version the L110 (fig. 363), required a faster rifling twist (FN recommended 1 turn in 7 inches) in order to stabilize."

i. e. it wasn't only to stabilize the tracer round.

"the 1 in 9" chrome lined is the best and longest lasting compromise we have found"

Even Bushmaster calls 1/9 a "compromise".

Would be nice to get our hands on the: Fabrique Nationale Herstal, Belgium Improved Ammunition 5,56x45. FN Report No. TW7, dated October, 1980 (cited in The Black Rifle Bibliography, p. 397).



I'm not an expert BUT there are many other sources out there for info. on the M16/AR15 & the 5.56mm NATO cartridge than the book you cite.
"The Black Rifle" isn't the the be all end all book!

Your ignoring the development history (& marketing!) of FN's M240 SAW . That & the tracers developed (& the SS109) for it have a lot to do with the 1x7 twist.

1x9 is a compromise, I don't think anyone will argue that, 69gr or less it's fine

it all depends on one's ammo selection
Link Posted: 10/16/2002 6:05:20 AM EDT
[Last Edit: 10/18/2002 12:47:59 PM EDT by SanchoPanza]
Troy, NO offense meant, but FN, who has much more credibility than you, says 1/7 is best for SS109, compared with 1/9 (best for neither & 1/12 (best for M193).

So, it seems that we disagree as to what is the "ideal" twist rate for SS109, AND it would seem that the 1/9 is a drum roll ...compromise between the best for SS109 (1/7), and the best for M193 (1/12).

This does make 1/9 good for commercial applications, for those who shoot SS109 (M855) and M193, and want the best for neither. (Don't think even you will argue that 1/12 is best for M193.)

Bushmaster, in Volume XVII of their Catalog, p. 2, said "We have found that the 1 in 9" twist gives the best results using either SS109 - 63 grain or standard M193 - 55 grain ammo,..." ( realize part of what is meant by best results is less wear in 1/9 with SS109, than with 1/7 with SS109).

This, then, per Bushmaster, is the compromise barrel. The words of Bushmaster, not mine.

In other words, the premise of your last post has yet to be proven.

i. e. until you prove FN (the chart previously cited), is incorrect, you've not a leg to stand on.

So, disprove the FN chart, please. Shall I scan it Be specific! Simply posting a bunch of links, as if I've never seen them, or are one of the great unwashed, or a greenpea won't work. I've been around this site, the AR15-L, and all the versions of the BB, since 1997, iIrc, and around M16A1 & AR15 (SP1) since 1979.
Link Posted: 10/17/2002 3:08:30 AM EDT

Originally Posted By DevL:
Please remember that the WEIGHT of the bullet is not what is important but the LENGHT of the bullet that matters. The LONGER the bullet the TIGHTER the twist needed to stabilize it. The DENSER the medium the FASTER the twist.

So the military started out with 1/14" for the M16. But in COLD air which has a greater DENSITY the bullet was not stable. They tightened the twist to 1/12" to stablize that LENGTH of bullet in all air DENSITIES we find on earth. Then they designed a longer 62 grain round. It required a twist of 1/9" to stabilize it. However the tracer rounds had a less dense material in them and were LONGER even though it was similar in weight. So the twist needed to be 1/7" to stablize the LONGER bullet. Heavy match bullets are LONG and require fast rates of twist to be stable. The heavier bullet the tighter the optimal twist will be if similar construction is used. To fire a 55 grain steel bullet would require a faster than 1/12" twist because the steel is not dense and the bullet would have to be LONGER than a lead 55 grain bullet.

If a bullet travels though VERY DENSE materials like water or body tissues it will become unstable and try to do what is natural and travel heavy end first. Thus they yawing you get with most rifle bullets. This is also why pistols that can be fired under water but are designed for shooting through the air become unstable after a short distance and the bullets veer off in a random direction.

I hope this explains twists and gyroscopic stability for you



OK I guess you did not read what I posted earlier so here it is again.

BULLET LENGTH IS THE IMPORTANT FACTOR.

I dont give a rats ass what FN has to say about it becuase the laws of physics are the laws of physics. The LONGER tracer round does NOT use an SS109 bullet. YES FN IS WRONG in this case! There I said it. Everyone here knows it and you are the only one who seems to think that the LENGTH of the SS109 is not stabilized in a 1/9 twist. I dont know why it is some people read something and think its the truth NO MATTER WHAT. The 1/7 twist does not have more inherant accuracy than the 1/9 shooting SS109 projectiles. If anything the 1/9 is MORE accurate than the 1/7 shooting SS109 bullets.

Hell the book even says the tracer version of M855/SS109. THERE IS NO TRACER VERSION OF M855/SS109. There is M856 and it uses a bullet TOTALLY different than the SS109 bullet. Any book can have an error and FN let this one slip by.
Link Posted: 10/17/2002 3:33:51 AM EDT
Lemme tell you a story.

Once upon a time the US military wanted a new squad automatic weapon. It needed to be able to penetrate a helmet at distances greater than the 7.62 round could and have a daylight tracer round that could travel OVER 800 meters in daylight. The first round selected was a 6.0x45mm round. Well The military didnt want to add a new round just for the SAW and the 7.62 round meant a weapon that was too heavy. So the 5.56 round was selected. PROBLEM the 5.56 round could not meet the spec for over 800m tracer capability. They dug as huge a recess out as possible and made the round as long as they dared but the military requirement of over 800m in daylight could not be met. So the military adopted less stringent standards so the round could be used. The round was XM778 and the ball round was XM777. These were the rounds finally submitted to the NATO ammunition trials and although a 1/9" twist was needed to stabilize the ball ammunition the greater LENGTH of the tracer round required a FASTER TWIST. All of the work done on this tracer round and the twist needed to stabilize it goes back to the 70s. The army allowed the reduced standards for the tracer round in 1976. The ball round remained unchanged but because of the alterations done to make a 5.56mm tracer round travel 700-800m still lit caused the barrel rifling to be changed from 1/9" to 1/7".
Link Posted: 10/17/2002 5:47:46 AM EDT
DevL,

OK, based on your statement below, I guess you did not read what I posted earlier...

"Hell the book even says the tracer version of M855/SS109."

No it DOES NOT. So here it is again...

"The Black Rifle", p. 340, "the SS109, especially it super-long tracer version the L110 (fig. 363), required a faster rifling twist (FN recommended 1 turn in 7 inches) in order to stabilize."

FN says you are WRONG. Think I'll trust their data over your unproven case.

I never said SS109 is not stabilized by 1/9...only that is not as accurate as through 1/7, again per FN.

Some people think they are right, NO MATTER WHAT.

Again, wish I had the complete report, so I could see how they came to their conclusion.

Perhaps they made an error in their tests, perhaps their test methods were correct, proving their data.

But, without this report, their test methods and results are impossible to review.

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