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View Full Version : 1/7 vs 1/9


TonyKat
06-01-2008, 7:20 AM
What do you think are the pros and cons between the two options?

Satex
06-01-2008, 7:58 AM
Here you go: http://ammo.ar15.com/

uscbigdawg
06-01-2008, 5:42 PM
In general, for me, I have no need for a 1/7 barrel, except in my DCM rifle. But, it came with it, so...ya know. In most of my rifles, I run a 1/9. Basically, it's super versatile and happily spins bullets from 52's (although in some it doesn't like them) all the way up to 69's. While I have one that'll do well with 75's and 77's, it's just not a perfect match.

On my 1/8's, I only run either 55's, 69's and 77's. The most versatile is my 18" JP/Voigt rifle. .25 MOA w/ 69's and about .4 w/ 77's (the 77's are shot at 100 though and it groups way better at 300 and out). The 55's are used for under 100.

On my 1/7, it's again a purpose rifle. I shoot 69's, 77's and 80's through it but again, that's position shooting at known distances. Completely devoid of the dynamics of 3-Gun.

So, figure out what you want the rifle to do and then work up a bullet window from there. For instance I have one AR w/ a 1/12 barrel specifically for varmints. 52's are like laser beams out of this rifle!

Rich

duenor
06-01-2008, 6:06 PM
Regarding barrel twist. Many here advocate 1-9" twist. Currently the M16A2 and M4 both use 1-7", which allows the rifle to stabilize M193, M855, and tracer ammunition (yes I know it is banned in california, but if you plan to use your rifle for SHTF then some of it might turn up in a post-apocalyptic world). 1-9" is proven to have problems with tracer. Here is a little bit about twist from ammo oracle (http://www.ammo-oracle.com/body.htm). I have both and I prefer the 1-7". All shoot equally well for me well. If you really want to see rifle performance set appleseed targets at 25 yards and start shooting.


Q. Will M193 be accurate in a 1:7 or 1:9 twist barrel?
It may be marginally less accurate due to the fast twist rate, particularly in 1:7 twist barrels. Unless you're trying to use these rounds for benchrest shooting, though, it shouldn't be enough to matter.
A bullet's flight is disrupted slightly as it leaves the barrel and after traveling some distance, will "settle down" into an even spiral, similar to a thrown football. The faster a bullet is spinning, the longer it takes to settle down. The most accurate twist rate for any length of bullet will be just a bit faster than what is required to stabilize it for its entire flight path (1.3 SG). But note that bullet quality plays a much bigger part in this equation. A uniform bullet will spin true; a non-uniform bullet will wobble and be inaccurate. As a general matter when shooting M193 or M855 (as opposed to match ammo) its better to err on the side of a faster twist rate. Regardless, both 1:9 and 1:7 twists seem to shoot M193 and M855 very well.

-hanko
06-01-2008, 6:29 PM
FN wanted a 1 in 7 twist when they developed the SS109, Army apparently wouldn't change. At least that's what I've heard;)

I think it's barrel-dependent...I have a 1/7 Armalite target upper on an Armalite lower with PRS and an RRA 2-stage trigger. With a 6x scope I can get M193 consistently within an inch and a half at 100 yds, 62gr LC groups around 5/8 inch. Handloads around half an inch with 62gr fmjbt's, that's about my shooting limit. Next step is to play with some 70+ grainers and see what might happen.

-hanko

duenor
06-01-2008, 7:14 PM
it is interesting that nearly everybody and their mother insists that 1-9" is superior, but folks who have actually shot both like hanko and myself don't see too much of a difference.

now, if you are like the previous poster who works with rather obscure bullet weights (handloading) such as 52, 77, 66, etc, then it probably does matter. but in that case you probably would have multiple uppers, so it would all be an irrelevant question anyway.

1-7" is damn good, lets you shoots tracers, and stabilizes SS109, M183, and M855 just fine.

huck
06-02-2008, 7:12 AM
... and there's always the 1:8 223 Wylde from RRA. That's what I did. Shoots everything.

duenor
06-02-2008, 8:00 AM
indeed, the Wylde is a balance barrel.
but it is also in 223 and not 556
and...
it ain't cheap

huck
06-02-2008, 8:18 AM
indeed, the Wylde is a balance barrel.
but it is also in 223 and not 556
and...
it ain't cheap

The Wylde is in between .223 and 5.56 and is supposed to shoot both effectively.

bubbaskyjacker
06-02-2008, 10:17 AM
im tired of this post! not cause there is'nt any good info its just too many different openions,,, 1/7 too fast 1/9 too slow 1/8 ?? if you want long range, not good for varmits, the new question needs to be what is the best all around barrel. i like to go to the range and shoot at paper when im in the city, but when i get out to the woods i want to kill ground squirrils and shoot beer cans. and odds are im going to buy the cheap ammo cause ill be broke after my build. so does it really matter if we are not target shooting?

Satex
06-02-2008, 11:33 AM
I am tired of this post! not cause there isn't any good info its just too many different opinions

You know, when people don't have options they complain. Now you have too many options - so you complain as well ;)
The AR family is the closest thing to adult LEGO rifle. There are a gazillion combinations you should choose. You won't be able to build one rifle for all types of shooting. So... you build a few ARs!

duenor
06-02-2008, 11:57 AM
1/7, 1/8, 1/9....
we posted the information already... it's up there.

bottom line - DON'T WORRY ABOUT IT. BY THE TIME YOU GET GOOD ENOUGH TO KNOW THE DIFFERENCE BETWEEN THE BARRELS YOU WILL WANT ANOTHER AR ANYWAY.

(but personally I recommend 1/7)

Addax
06-02-2008, 12:26 PM
http://ammo.ar15.com/#whattwist

Q. What twist rate do I want for my rifle? Probably 1:9, but it depends on what kind of bullets you intend to shoot.

Special purpose rifles often have uncommon twist rates. For example, if you are building a varmint rifle and want to shoot the short 35 grain, 40 grain, and 50 grain bullets, a 1:12, or even 1:14 twist would be best. On the other hand, long range High Power shooters often select 1:8, 1:7.7, 1:7, or 1:6.5-twist barrels to stabilize the long 77, 80 and even 90 grain bullets used for 1,000 yard competition. Additionally, new testing of heavier rounds (68-77 grains) seems to show that they perform very well in simulated tissue and may be a better defensive choice than 55 grain or 62 grain rounds. The majority of shooters, though, typically shoot bullets of 50 to 69 grains in weight (note that the 62gr SS-109/M855 bullet is as long as a 71 grain lead core bullet) and should select 1:9 twist barrels. At typical .223 velocities, a 1:9 twist will stabilize bullet lengths equivalent to lead-core bullets of 40 to 73 grains in weight.

1:12 twist rifles cannot stabilize SS-109/M855 bullets and 1:7 twist rifles are slightly less accurate with lighter bullets and will often blow apart the thin jackets of lightweight varmint bullets. The 1:7 twist is used by the military to stabilize the super-long L-110/M856 tracer bullet out to 800 yards, but unless your plans include shooting a significant amount of M856, the 1:9 twist rate is better suited for general use.

There is, of course, an exception: if you want to use loads utilizing the heavier, 75-77 grain match bullets currently used by Spec-Ops troops and other selected shooters, you'll want a 1:7 twist barrel. Although military loadings using these bullets are expensive and hard to get, some persistent folks have managed to obtain a supply, and will need the proper barrel twist to use them. Anyone who foresees a need to shoot this ammo should consider a 1:7 twist barrel.

Stormfeather
06-02-2008, 2:55 PM
I hated 29 palms, and I wouldnt want to be with 1/7, However, I was with 1/9 back in the day, and they was a KATN unit!

http://www.i-mef.usmc.mil/div/7mar/1bn/

http://www.iimefpublic.usmc.mil/public/iimefpublic.nsf/unitsites/1stbat_9thmar

duenor
06-02-2008, 6:44 PM
Again, I personally prefer 1/7. But that's just me.

will0861
06-02-2008, 6:57 PM
This seems to be a Ford vs. Chevy argument. There will be no clear winner, since each twist has it's own merits for different applications. If it works for you, go with it. If it doesn't, well you have an excuse for a new rifle, or upper.

In general it seems that the faster twists work better with heavier bullets. However, I know that is not always the case. I think your shots will be affected much more by the wind than by the twist of the barrel. So learn to shoot well, keep trying a combo that works for you.

ar15barrels
06-02-2008, 9:58 PM
I would rather have a 1:12 for it's improved accuracy with cheap bullets.

bubbaskyjacker
06-04-2008, 6:11 PM
"Bullets must have enough “spin” (RPM) when leaving the bore in order to fly “true”. Remember – bullets begin to slow down (in RPM and velocity) from the moment they leave the bore – so they must have enough “spin” from the start so that they remain spinning enough to fly true over the course of their trajectory – otherwise – if they aren’t spinning enough – they will start to wobble off course – which can result in a complete miss. (Remember – “misses” are bad.)

Barrel twist rates are calculated using the caliber of the projectile and the length of the projectile. Most think in terms of “weight” of the projectile that determines twist rate – but it is really the length. And in general terms – the longer the bullet – given the same caliber – the more it will weigh – but the truth is – you could have two bullets that weigh the exact same amount – but if one has an “aluminum” core – it will be longer than the one with a lead core – so the lighter bullet – BECAUSE it is longer – will require a “tighter” twist rate than the heavier/shorter one will.

The M16 started off with a 1x14” twist – which is enough to shoot 55 grain bullets – as long as the temperature of the air was above freezing. If the temp was below freezing – the air density was such that the 1x14” twist was too slow and the bullet lost its spin too fast resulting in misses.

So the military changed the rate to 1x12” – which solved the problem.

Then comes along the SS109/M855 62 grain round – which – since it is a longer bullet (because it is heavier) requires a 1x10” to stabilize. Problem was – the “tracer” ammo M856 is even longer than the “ball” round of the SS109/M855 ammo cause they packed it with enough tracer compound so the bullet would trace all the way out to 800 meters – which it almost twice as far as the older tracer ammo that burnt out at around 450 meters. Consequently – this “newer” tracer ammo is a LONG bullet – and requires a 1x6” twist rate. So the military compromised on a 1x7” twist rate for the new ammo.

Shorter (which USUALLY means lighter) bullets can be fired in barrels with tighter twist rates than in necessary – but longer (which USUALLY means heavier) bullets cannot be shot in barrel twist rates that are slower than what they need. So – the most versatile barrel twist rate is one that is tighter – as it will shoot all bullet lengths/weights.

An example of what happens when uses a longer/heavier bullet in a too slow twist rate is shooting a SS109/M855 62 grain bullet in a 1x12" twist barrel. What will happen is right around 100 meters the bullet has lost too many RPM's and will actually start flying end over end - with horrible accuracy. The bullet may strike "sideways" - which is called "key-holing" - leaving a sideways imprint of the bullet. Hitting a body with a "key-holing" bullet aint bad - the bad part is the bullet won't go where it was aimed - so you only hit with a "fluke". Since our goal is to hit when we are aiming at something - key-holing is BAD. MIssing is WAY TOO easy with bullets that fly true - missing is almost garaunteed with bullets that don't fly true.

Bushmaster – which was really the first company to start building AR’s in a big way – looked at the available ammunition back in the 80’s when they started – and back then – 62 grains was “heavy” for .223’s. Well – the 62 grain lead projectile only “needs” a 1x10 twist to stabilize – and since some 68 and even 69 grain projectiles were on the horizon – they figured – what the heck – lets have our barrels be 1x9” twist. No one is going to be shooting heavier/longer bullets than 69 grains – so 1x9 twist will be fine. Remember – back then most bullet weights/lengths were in the 40-55 grain area.

Bushmaster soon became the “leader” in AR’s – and when more and more companies came on board – they “followed the leader” and had their twist rates be 1x9” also – which UNTIL the heavier bullets came along just a few years ago – worked out just fine.

Now – advance forward to just a few years ago when the war on terror started in earnest. The 62 grain bullet wasn’t cutting the mustard. Due to different manufacturing techniques of bullet manufacturers – some lots of the M855 won’t fragment they way some other lots of M855 will – and we all know that if the bullet doesn’t fragment – it doesn’t work as well as when it does fragment. Also – the “range” at which it will fragment is less than 200 meters. Couple this with the fact that the M855 bullet – since it has a lead and steel core – can NEVER be as accurate as a bullet that has an all lead core – making distant “sniper” type shots a lot harder.

So – SpecOps units started looking for a different bullet. (This is what started the ill fated attempt of the 6.8 SPC.) The military match shooters at the time were dominating the shooting matches using bullets that were 75-77 grains in weight. These bullets would allow our boys to make shots out to 600-700 meters with confidence of a hit – cause they are extremely accurate bullets. What the SpecOps boys found out – that in addition to being accurate – these heavy bullets FRAGMENTED when they hit most water based mediums (bodies). And they fragmented with much more “vigor” than the 62 or even the 55 grain bullets – cause – since they were heavier/longer – they had more material to fragment with! AND – they are fragmenting at ranges far in excess of 200 meters.

These heavier bullets are doing such a good job – that the 6.8 has since died on the vine.

So if one is getting a new AR or just a new barrel – for SHTF purposes – it would be my advice to a 1x7” twist barrel. The 1x7” twist will allow you to shoot ALL 55 grain ammo, 62 grain ammo and the 75 or 77 grain ammo. What you won’t be able to shoot is the thin jacketed 40 grain ammo – but no one would use that for SHTF purposes anyway! In other words – you lose NOTHING by going to the 1x7” twist barrel – but you GAIN the versatility of being able to use ANY “fighting bullet” made for the 5.56 family of firearms. So my question would be – WHY LIMIT YOURSELF?? You may not have any of the 75 or 77 grain ammo - but why close the door on EVER using it?? Think in these terms - more and more LE units are moving to these rounds - the whole US military is looking at these rounds (because of the great success the SpecOps community is having with these rounds) - so this ammo is only going to be more prevalent as time goes on. DON’T GET A NEW BARREL/UPPER that can’t shoot these new rounds or you may live to regret it!

If your barrel has a 1x12" twist - you are limited to 55 grain ammo.
If your barrel has a 1x9" twist - you can shoot either the 55 grain or 62 grain (actually up to 69 grains reliably)
If your barrel has a 1x7" twist - you can shoo the 55 grain, 62 grain, 75 and 77 grain - even all the way up to 80 grains reliably

As far as ammo choices:
First choice BY A LONG MARGIN would be the 75 or 77 grain ammo – it fragments beautifully from point blank out to many hundred meters.

Second choice would be M193 or equivalent 55 grain ammo – if fragments reliably from point blank to around 150 +/- meters.

DISTANT third choice would be the SS109/M855 62 grain ammo – which is not a reliable fragmenting round at any range.


Hope this helps,

cheers

tire iron" this is not from me its from tire iron from www.americanminuteman.net. it sounds pretty good?

will0861
06-04-2008, 6:16 PM
That is good info. I don't mean any disrespect, but where did you get your information?

duenor
06-04-2008, 6:30 PM
look at the bottom for the link
as i said before, 1-7" has my vote of confidence. and once again, there really is no difference for most shooters, and even for most situations.

will0861
06-04-2008, 7:10 PM
I guess I should open my eyes a bit, sorry about that. Thanks again.

FlyingPen
06-04-2008, 7:23 PM
I would rather have a 1:12 for it's improved accuracy with cheap bullets.

Stop tempting me man.

Anyone care to hazard a guess on how much less accurate 22LR minimags are out of a 1/7 than a 1/12 at 25 to 50 yards?

ar15barrels
06-04-2008, 7:47 PM
1:12 is optimum for 55gr ammo which is just perfect as that's all MOST people ever shoot anyways.
Why have extra twist which just throws in-consistent bullets further out of the group if you don't need the extra twist?
If you need to shoot 77's, you can always have another gun or upper for them anyways.
1:12" is perfect for most casual plinking, target shooting or competetion.
The only people that REALLY need a fast twist are long range shooters or guys shooting at "soft targets" (people).

FlyingPen
06-04-2008, 7:54 PM
I wish Noveske made a 1/12 16" midlength.

In my search all I've found was White Oaks with a 18" 1/10 and like you said, CMMG with a 1/12 16" which is at least midlength. I really wanted a Noveske barrel for my next upper though.

So 1/12 won't properly stabalize 62gr Silver Bear will it? It looks like pretty good value plinking ammo for cheap.

ar15barrels
06-04-2008, 7:55 PM
So 1/12 won't properly stabalize 62gr Silver Bear will it? It looks like pretty good value plinking ammo for cheap.

Don't shoot crappy ammo.
Shoot brass cased 55gr ammo with copper jacketed bullets at the very least.

FlyingPen
06-04-2008, 7:58 PM
Don't shoot crappy ammo.
Shoot brass cased 55gr ammo with copper jacketed bullets at the very least.

Only if you're paying! :D

I think the cheapest is Privi for $350/100 + shipping... quite a bit more than $235/1000.

What's the reason why 1/12 is more optimal for M193 than 1/7?

ar15barrels
06-04-2008, 8:05 PM
Only if you're paying! :D

I think the cheapest is Privi for $350/100 + shipping... quite a bit more than $235/1000.

What's the reason why 1/12 is more optimal for M193 than 1/7?

If the price is an issue, start reloading.
You are going to want to load for your 308 as well.
You can spend $1000 on a good setup and then load 223 for $130 per 1000.
That means the press pays off in 5000 rounds or less of 223.
308 will run you around $10 per 20 with SMK's.
500 rounds of match grade reloads would pay off the reloading setup.

The reason that 1:12 is optimum for 55's is that it has JUST enough twist to stabilize them in all conditions.
Twist rate is a double-edged sword.
First, you need enough twist to stabilize a bullet.
Second, you don't want to twist them a lot more than they need or groups open up due to bullet in-consistencies.
You notice the effects of too much twist the most with cheap bullets.
Match grade bullets are more consistent so they don't show as much accuracy loss due to being spun faster than required.
Benchrest shooters run the absolute slowest twist rates that they can get away with to shoot the absolute smallest groups.
1:13 or 1:14 is most common for benchrest.
Slower twists also distort the bullet less and give higher velocities for the same chamber pressures.

Builder
06-04-2008, 8:33 PM
If the price is an issue, start reloading.
You are going to want to load for your 308 as well.
You can spend $1000 on a good setup and then load 223 for $130 per 1000.
Of course, that's good advice. I found a used old Lyman set up locally, but it works. Look around, you might just get lucky. There are some on ebay; some used, mostly new. Old used equipment just leads to new equipment. :D
Enjoy,
Builder