View Full Version : 1/7 vs. 1/9
mattpittinger
07-17-09, 13:40
What are the pros and cons of building a rifle with 1/7 or a 1/9 twist. I don't see the advantage of going to a 1/7 because 99% of what I shoot is 55gr. Is there something I am missing? Any input would help
If you only shoot is 55 grain there would be no advantage to a 1/7 over a 1/9.
I chose 1:7 so I could use any ammo out there in case the SHTF and ammo is hard to come by. I am a pessimist by nature.
I am a pessimist by nature.
I see it as more a "realist" position myself. [/thread drift] ;)
There's no advantage to a 1/9 twist
1/7 will fire 50-80 just fine, and it's been my experience that even 45gr fires perfectly fine.
You realize the m16/m4 are 1/7, right? m193, the most-fired cartridge in the Army, is 55gr... shoots as accurately as any twist can shoot it.
The only evidence that I've seen of 1/7 having any limitations whatsoever is an occasional person saying that it's possible 1/7 wont stabilize <50gr ammo- possible. i've never seen it, i've never heard anyone else say they've seen it, never read anyone post here that they've seen it, nor read any specific instances published. I've never even heard lame-ass gunshow dealers pawning 1/9s give any specific examples- guys who are known for lying.
1/9, on the other hand, has very well documented and widely known limitations...
why would anyone ever get a 1/9? 1/7 is the only twist i use. my 5 current guns are 1/7, two of which have fired cheap underpowered PMC 45 .223 ~1.25 MOA- without trying very hard. aside from 75gr training TAP, i fire xm193 pretty much exlusively. no problems whatsoever.
What is going to be your purpose/use for this gun?
That might give some answers for others to go by.
But BKB0000 gave you a good reason for 1/7 which were the same ones I based my decision on.
1/7 got my vote for those reasons.
SWATcop556
07-18-09, 02:19
Thereis no advantage to shooting a 1/9 even if you think you will only ever shoot 55 grn.
Why limit yourself on ammo selection. Who say tha one day you find a "too good to pass up" deal on a case or two of 75 grn ammo.
"Damn I would love to buy that but my barrel won't shoot it........"
Parabellum9x19mm
07-18-09, 02:40
why do many manufacturers even still use 1/9 as their primary twist for their barrels?
their line is that "1/9 doesn't wear as fast as 1/7".
but these manufacturers KNOW that 99% of their customers are likely to never shoot out one of their barrels regardless of the twist rate.
i just don't get it.
is it because its just cheaper for them, because the customers who buy the varmint type ARs want 1/9, therefore they save money if they make all their ARs with the same twist rate?
that's probably it. the same reason they try to sell us chrome lined 16" HBARs :rolleyes: because the profit margin is higher.
Bread is People
07-18-09, 15:50
What about 1/8 twist rate? I believe that is what the S&W 5.45 barrels have, why not in a 5.56 barrel?
I still vote for 1/7 though; it's blue on "the chart" for a reason.
One advantage that I can see is that a 1/7" will more than likely be HP/MPI tested and inspected and a 1/9" more than likely not. In addition though some 1/9" will shoot the heavier bullets there is no guarantee the one you get will. A 1/7" most likely will and shooting 55gr. is no problem. Seems like the 1/7" is the smarter choice.
constructor
07-18-09, 18:33
quoted from the 6mmBR website .223/5.56 article.
Overall, what twist rate is best? For varminting we like a 12-twist. The slower twist will give you a bit more velocity, and minimize the risk of jacket failure at high rpms. For general use, an 8-twist barrel will let you shoot the excellent 77gr and 80gr Sierra MatchKings and nearly all varieties of non-tracer milsurp ammo. We'd only select a 1:7" or faster twist barrel if we had a need to shoot the 90gr VLDs.
Out to 100 yards it hasn't appeared to me to matter either way. 3 of my 4 are 1:7 and they do deliver 55 grain as well as my 1 and previous 1:9's. (shrug)
Oddly, I've run into two very experienced long range competitors that have told me very seriously that 1:7 can over-spin 55 grainers till they literally spin apart in mid flight and never reach the target. They actually seem to believe this.
LonghunterCO
07-18-09, 19:48
One of my first handloading experiment with a 1/7" twist was with a batch of Speer soft nose rounds (not sure as to the weight but they were in the mid to low 50's). They spun apart. I was shooting at the 100yd line, prone, and I had a five round target with a couple of (non-round) jagged holes/tears and pieces of jacket stuck in the wooden target stand. With that said I have shot 52gr match handloads on up in it without issue. I think that the problems is with lighter jacketed rounds pushed fast.
1/9" does not offer any advantages over 1/7" other than there are more available barrels in it. Many on the lower end of the quality spectrum.
Thomas M-4
07-18-09, 20:02
Out to 100 yards it hasn't appeared to me to matter either way. 3 of my 4 are 1:7 and they do deliver 55 grain as well as my 1 and previous 1:9's. (shrug)
Oddly, I've run into two very experienced long range competitors that have told me very seriously that 1:7 can over-spin 55 grainers till they literally spin apart in mid flight and never reach the target. They actually seem to believe this.
They are using longer barrels which will achieve higher velocities = more bullet RPM.
Also varmint bullets are very thin jackets and are designed to immediately fragment when they hit something.
Here are some cool vids of Barnes varmint grenades .224 cal hitting a seedless grape and a 6mm hitting a cherry tomato http://www.barnesbullets.com/information/high-speed-video/
One advantage that I can see is that a 1/7" will more than likely be HP/MPI tested and inspected and a 1/9" more than likely not.
Good point, and the ones that are marked tested on certain brands is via a batch testing procedure, not individually.
Maybe not of consequence for you, but the 1:9 barrel did NOT stabilize RRLP and one other frangible/training ammunition at all, with keyholing at 25 yards when I tested it last year. There was no keyholing exhibited by the 1:7 twist out to 50 yards, the longest range available to us that day. Several rifles with both twists were checked for function, etc. with the same ammuntion.
I chose 1:7 so I could use any ammo out there in case the SHTF and ammo is hard to come by. I am a pessimist by nature.
The heavyweight gucci ammo was the first to dry up, and the least frequently appearing. On the other hand, I can walk into several retailers and buy 36-45gr varmint loads by the thousands if I chose. It might also be interesting to note the production ratios of heavies to lights. One manufacturer reported that for every round of 70+ they load, they load some ~25,000 of others. Nearly that in another, and I suspect that split or greater is the norm.
The only evidence that I've seen of 1/7 having any limitations whatsoever is an occasional person saying that it's possible 1/7 wont stabilize <50gr ammo- possible. i've never seen it, i've never heard anyone else say they've seen it, never read anyone post here that they've seen it, nor read any specific instances published. I've never even heard lame-ass gunshow dealers pawning 1/9s give any specific examples- guys who are known for lying.
Done it, and witnessed it, as have some other group members here. There are previous posts on the subject.
The gun of one member here, a Colt LE6920, will produce jacket core separations with some predicatability when shooting economy 55gr FMJ. Another lurking member, who I believe is running a 1/7 RRA, is a varminter who can pretty reliably shred the 36-52gr varminting loads.
The 1/7 vs 1/8 debate gets a bit silly, and their are more important attributes of the gun to sweat over. Most folks don't and won't shoot the heavies, and they shouldn't lose any sleep if they have a 1/9.
(It's in this debate that we should again make the distinction between owners and shooters. The former being far more in number than the latter.)
Heavy Metal
07-19-09, 10:31
I have a 1/7 twist Colt barel that will shoot Federal 50 and Win 45 grain hollowpoints fine.
Patrick Aherne
07-19-09, 11:57
If you will EVER shoot frangible ammo, you need 1/7" twist barrels. The 42-45 gr. frangible stuff is as long as most 80 gr. bullets. Out of 1/9" twist barrels, the frang stuff keyholes at 4-5 yards. There is NO reason to buy a 1/9" twist barrel for any home defense or duty use.
Our agency has at least 30-40 personally owned firearms that are 1/7. Amongst that group 99% could not even tell you what that even meant. We shoot the 55 grn fmj for the majority of our practice. There have been no issues as a result in tens of thousands of rounds. We do have to remind them to zero with their actual duty ammo though. Most folks reading this here would take that for granted, but in the real world...... :rolleyes:
Another vote for there is no reason to purchase a 1/9 barrel.
One advantage that I can see is that a 1/7" will more than likely be HP/MPI tested and inspected and a 1/9" more than likely not. In addition though some 1/9" will shoot the heavier bullets there is no guarantee the one you get will. A 1/7" most likely will and shooting 55gr. is no problem. Seems like the 1/7" is the smarter choice.
It looks like the 1/7 is becoming more common with the lower grade barrels.
I have shot bullets down to 45gr in with the 1/7 with no problems.
Here is a video of a 1/7 shooting 35gr and 40gr bullets. You will notice that the 35gr bullets are disintegrating in flight a few feet away after being shot. The 40gr are doing fine at 300 yards.
http://www.youtube.com/watch?v=GTJaNHjEa_k&feature=channel_page
My 1/8 barrel gets great groupings from 45 gr bullets.
decodeddiesel
07-21-09, 10:10
I have personally tested 40gr hollow point rounds from my 14.5" LMT with a 1/7 twist. At least 2 out of 5 rounds would suffer jacket seperation some 25-30 meters in front of the weapon.
Remember at that velocity and twist rate the bullet is spinning at around 350,000 rpms. Now think about that for a minute. The centrifugal forces on that little hunk of lead and copper are huge. The problem you run into is when a bullet manufacturer uses a thin copper jacket on the round (as most varmint rounds do) and that jacket ruptures.
Now with that being said I think any and all serious use weapons should have either a 1/8 twist or a 1/7 twist. That same LMT will shoot 55gr M193 very well (around 2 MOA), and shoots 75gr T2 TAP even better. :D
I know heavy bullets are not as common as light bullets in .223, but honestly I think the lighter rounds are just not very suitable for use against human targets and you are really limiting your ammo selections when going with a 1/9 twist.
I've got both 1:7" and 1:9" bbls.
The most accurate barrel I have is a Wilson Combat 1:9", 5.56 NATO, 4140, 16", m4 contour. I won't blow-up 40s. It shoots 55gr Sierra FMJs into .75" at 100 yards scoped. It has a slight bias for 68 gr BTHPs shooting them into about .5" at 100. It shoots 75s on par with my 1:7" 6920.
The original intent of this barrel was to use on a coyote rifle, not a fighting gun.
So would one have the advantage if he reloaded to be able to slow down the 35s,and 40s with a 1:7 so as not get them going so fast as to "Blow Up"? But still have the advantage of the heavier ones in 1:7.
Comments please, pro's and con's.
So would one have the advantage if he reloaded to be able to slow down the 35s,and 40s with a 1:7 so as not get them going so fast as to "Blow Up"? But still have the advantage of the heavier ones in 1:7.
Comments please, pro's and con's.
If you slow them down so much, will it reliably cycle? Maybe, maybe not.
I wouldn't think that you could get the tinier varmint rounds to reliably cycle a carbine AND not regularly self-destruct in mid-air. More importantly, why would you want to shoot such rounds through a 1:7 barrel?
-B
save varmint rounds for varmint guns... varmint guns are a totally different ball of wax, just like space guns.
For Varments that's why I keep my 22 rf and 22-250 for, but even my rem 700 22-250 I shoot 55 grain there too for PDs. I like seeing two parts dog go 20-30 feet up in oposing directions. Then when we get bored we bring out the AKs to make it a little bit more challenging. Even when I take my AR I shoot 55s there too.
There's no advantage to a 1/9 twist
1/7 will fire 50-80 just fine, and it's been my experience that even 45gr fires perfectly fine.
You realize the m16/m4 are 1/7, right? m193, the most-fired cartridge in the Army, is 55gr... shoots as accurately as any twist can shoot it.
Are you kidding me? M855 is the standard issue 5.56 round. I only ever saw M193 at ranges and it had old headstamps. M193 is only produced still because there are M16A1s in use in the Air Force and in war stock.
Are you kidding me? M855 is the standard issue 5.56 round. I only ever saw M193 at ranges and it had old headstamps. M193 is only produced still because there are M16A1s in use in the Air Force and in war stock.
855 is the standard issue duty round. ranges are where most of the army's ammo gets burned up. it's been a few years since i got out, but when i was in, if we were shooting at cardboard or plastic, we were shooting m193.
M855 is the standard round for combat usage. There is plenty of M193 still being produced for punching paper. I have seen .MIL issue with headstamps as recent as the last few years.
Are you kidding me? M855 is the standard issue 5.56 round. I only ever saw M193 at ranges and it had old headstamps. M193 is only produced still because there are M16A1s in use in the Air Force and in war stock.
decodeddiesel
07-22-09, 09:27
855 is the standard issue duty round. ranges are where most of the army's ammo gets burned up. it's been a few years since i got out, but when i was in, if we were shooting at cardboard or plastic, we were shooting m193.
That's true in every unit I was in except the 101st. We ALWAYS had M855 for training/sandbox issue. We even started to see Mk. 262 Mod. 1 trickling in during my second tour in 05-06.
I agree with you though, why bother with anything less than 1/7 or 1/8.
That's true in every unit I was in except the 101st. We ALWAYS had M855 for training/sandbox issue. We even started to see Mk. 262 Mod. 1 trickling in during my second tour in 05-06.
I agree with you though, why bother with anything less than 1/7 or 1/8.
I was in the 82nd and only saw M193 at a range twice (and it wasn't at qual ranges either) and was even issued M855 only during basic in '01. Supposedly the only reason we had M193 at a few ranges was because OEF had just kicked off and they were trying to use up the stuff that wasn't going to be used over there. I prefer 1/7, but the vast majority of my ammo stockpile is XM193 and M855 so a 1/9 will get it done there. However I would never want to be unable to fire the 75/77 grain stuff.
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