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Posted: 11/1/2005 6:30:53 AM EDT
I've read on ARFCOM a long while back that some people have problems with 1/9 barrels stabilizing 77gr SMK's. I am going to buy a new 16" carbine but I am looking at a 1/7 twist specifically to shoot this bullet. I have a line on a 1/9 chrome-lined upper but I'm hesitant to buy it based on what I've read here IRT 77gr bullets. Will a RRA 1/9 chrome-lined barrel reliably stabilize 77gr SMK's?
Link Posted: 11/1/2005 6:34:19 AM EDT
[Last Edit: 11/1/2005 6:35:52 AM EDT by bigbore]
Link Posted: 11/1/2005 6:35:23 AM EDT
[Last Edit: 11/1/2005 6:36:39 AM EDT by rob78]
Based on what I've seen (limited mind you) a 1/9 twist barrel has problems stabilizing a bullet as long as 68grains (Bushmaster and a Rock River barrel using Ultramax Reman. 68gr.). If I were looking for a barrel whose primary purpose was to fire 77gr. (long OAL) bullets; I'd get the 1/7 twist without a shadow of a doubt.

Why take chances?

ETA: Unfortunately, i don't have any pictures
Link Posted: 11/1/2005 7:09:20 AM EDT

Originally Posted By redleg13a:
I've read on ARFCOM a long while back that some people have problems with 1/9 barrels stabilizing 77gr SMK's. I am going to buy a new 16" carbine but I am looking at a 1/7 twist specifically to shoot this bullet. I have a line on a 1/9 chrome-lined upper but I'm hesitant to buy it based on what I've read here IRT 77gr bullets. Will a RRA 1/9 chrome-lined barrel reliably stabilize 77gr SMK's?



If you are looking to shoot at distance, or of you plan on mainly using heavier bullets, go with the 1:7 so you can keep all options open.

As Bigbore is nice enough to point out, the 1:9 seems to be highly underrated by many people on this board, and most of those naysayers have no idea what they are talking about.
Link Posted: 11/1/2005 7:35:39 AM EDT
[Last Edit: 11/1/2005 7:38:39 AM EDT by Da_Bunny]
Understabilizing would show up at ranges beyond 100 yards. I'm happy with my 1:9 barrels, but I have a couple 1:7 that I use for 75-77 gr.

Nice shooting, bigbore.
Link Posted: 11/1/2005 8:10:45 AM EDT
[Last Edit: 11/1/2005 8:11:13 AM EDT by rob78]
Whether or not it was destabilization...i'll leave to you to decide.

68gr reman. Ultramax out of two different ARs, both with 1/9 twist rates. Neither was "inaccurate" but the holes in the target were ragged (but not keyholing).

Same ammunition with a 1/7 twist BM barrel...the holes appeared to cut with a paper puncher ala' wadcutter.

were the barrels unable to stabilize the longer bullet as well...I maintain yes. Now i know it's less than scientific, but it was what I observed.

ETA: the distance was 100yds.
Link Posted: 11/1/2005 8:43:14 AM EDT
Link Posted: 11/1/2005 8:57:00 AM EDT
[Last Edit: 11/1/2005 8:58:40 AM EDT by Ridge]

Originally Posted By rob78:
Whether or not it was destabilization...i'll leave to you to decide.

68gr reman.Ultramax out of two different ARs, both with 1/9 twist rates. Neither was "inaccurate" but the holes in the target were ragged (but not keyholing).




This is your problem.
Link Posted: 11/1/2005 9:11:02 AM EDT
I've had far better luck with 75gr Hornady than with the 77gr SMK in 1/9 barrels.

If you're getting a barrel specifically to shoot 77SMK's, get a 1/8 or 1/7 IMHO.
Link Posted: 11/1/2005 9:11:53 AM EDT
Few observations here:

1. that appears to be a red box of 75grn. Hornady TAP
2. the yellow box apears to be 77grn. Nosler bullets (not the SMK)
3. no optics on either rifle (w/ extraordinarily tight groups for open sites at 100 yards)
4. from ADCO's own web-site, it apears they have trouble with the differences between "chrome-lined" and "chrome-moly"....

www.adcofirearms.com/rockriver/rrauppers.cfm?page=rra

"pic of upper here"

A2 CAR
chrome lined 1734
$450.00
Complete w/bolt, carrier, and charging handle
5.56 chamber, 16" 1:9 chrome moly Wilson barrel.

YMMV, but I believe there's a difference between chrome-moly and chrome-lined.

Mike

ps - one thing to consider here, dealers w/ 1/9 twist barrels and products in stock have good reason to overstate the abilities of their products.....food for thought.

I swapped all my 1/9 uppers out for 1/7s (2 were RRA uppers/chrome-moly, 1 Bushmaster/chrome-lined) not because they wouldn't shoot the 77grn. SMKs, they shot'em, they just didn't shoot the group sizes depicted above, wereas my 1/7 twist uppers (from CMMG and LMT) shoot knots at 100 yards using factory bluebox BH 77grn. SMKs .

Link Posted: 11/1/2005 9:15:52 AM EDT
1/9 will fling a 77 like a boomerang and hit you in the ass!
Link Posted: 11/1/2005 9:20:00 AM EDT

Originally Posted By Ridge:

Originally Posted By rob78:
Whether or not it was destabilization...i'll leave to you to decide.

68gr reman.Ultramax out of two different ARs, both with 1/9 twist rates. Neither was "inaccurate" but the holes in the target were ragged (but not keyholing).




This is your problem.



Is it? I didn't have this "problem" with the 1/7 barrel.

Accuracy didn't appear to be affected (at least to no great degree...I didn't break out the calipers).

BUT...fact remains that there was an observable difference. You can buy what you like...I'll stick to 1/8 or 1/7 twist for bullets as long or longer than 68grains.

BTW: Neither barrel was "shot out" and the "test" was in fact at the request of a friend who wanted to know if there was any discernable difference between the available twist rates.
Link Posted: 11/1/2005 10:41:10 AM EDT
I am definitely sticking with 1/7. Thanks for the discussion, folks.
Link Posted: 11/6/2005 5:00:05 AM EDT
[Last Edit: 11/6/2005 5:02:16 AM EDT by bigbore]
Link Posted: 11/6/2005 12:29:13 PM EDT
I was very skeptical on this, so I decided to make some tests.

I got very similar results today with my Bushmaster M4 14.5" 1/9" barrel as bigbore. I used 77gr SMK with 25gr of Vihtavuori N140 and CCI400 primers in Lapua case. Shooting distance was 150 meters.


MN
Link Posted: 11/6/2005 6:14:43 PM EDT
I used 77gr out of Bushmaster M4 upper in Iraq last year and wacked 15 wild dogs with no noticeable difference in accuracy. Stabilized fine out to 200 meters. I never fired on a target past that. Hit one dog at 175 meters running. That's good enough accuracy for me.
Link Posted: 11/6/2005 6:26:49 PM EDT
All three of my 1/9 barrels (14.5", 16", and 24") stabilize 75 and 77 grain ammo just fine.
Link Posted: 11/6/2005 6:57:00 PM EDT
My experience with 5 different 1-9 twist rifles is that they will stabilize 75 and 77 grain bullets. I have shot the Hornady 75gr BTHPat 600 yards through a 26" 1-9 twist Wilson barrel on a Winchester M-70 and hit the x-ring on a highpower target with boring regularity (6" x-ring). These were magazine length loads with 24 gr of Varget. My 16" ,1-9 twist ,chrome lined ,lightweight barreled ,CAR length gas system, AR will shoot scores of about 97 -98 with about 4 X's at 200 yards (3" x-ring, 7" 10 ring) and about 95-96 with 2 or 3 x's at 300 yards ( same size x and 10 ring. This with 77gr Sierra's and 24gr of Varget. The biggest limitation with the CAR is the short sight radius which makes focus on the front sight a challenge. I have also shot 80gr Sierra's at 1000 yards ( not a mag length round ) through a 1-8 twist barrel with no bullet stabilization problems. All that being said, a 1-9 will get the job done, but a 1-7 doesn't hurt a thing and may help in cold weather when velocity is down.
Link Posted: 11/6/2005 7:08:30 PM EDT
My two 1/9 Bushmasters, one 20", and one 14.5" shoot both the 77 grain and the 75 grain rounds great, the farthest I've shot them is 300 yards, and they still outshot 55 grain XM193 and XM855. Out of my 20" both rounds will shoot under an inch at 100 yards if I do my part, using a 9X scope.
Link Posted: 11/6/2005 7:47:35 PM EDT
Let's try this again. Seems U have to retype two times to post. I must be the exception to the ballel twist rule. With my Olympic Arms UltraMatch barrel in 1 in 8.5, I have shot 80 grain Sierras at 600 years for a 97-6X and NO keyholing. Go figure.hug.gif
Link Posted: 11/6/2005 7:51:56 PM EDT
I was introducing a new shooter to the joys of High Power and let him try some Hornady 75 grain TAP out of his 1-9" Twist AR at 600 yards. Stuff shot just fine through his rifle, and he was immediately hooked when that first "X" came up.
Link Posted: 11/7/2005 5:45:54 AM EDT
Link Posted: 11/7/2005 9:07:52 AM EDT
1/9 barrel understabilised...

More likely with lower pressure ammo than with higher pressure ammo.
More likely with a barrel with high round count.
More likely in cold weather due to velocity loss and air density.
More likely at sea level than high altitudes.
More likely with shorter barrels than with longer barrels due to higher RPMs with longer barrels.
More likely with copper fouling than freshly cleaned.

Take a 1/9 SBR, with 5k through her, in the winter, at low altitude, with no copper solvent cleaning in the last 1k or more, using 75 grain .223 pressure ammo and you will ilkely have instability problems. The more of those factors you remove the closer you get to it happening 0% of the time.

If your barrel is fresh, clean, 16" or longer, using 5.56 pressure ammo, etc you are unlikely to have problems.
Link Posted: 11/7/2005 10:04:30 AM EDT
[Last Edit: 11/7/2005 10:11:25 AM EDT by Combat_Jack]
I have yet to see a test where someone uses heavy bullets in cold weather and checks to make sure they remain stabilized at a distance. Until I do, I will stick with 1/7, because I know it works.

If I get time this winter I may test it. Probably get some shots downrange in 0* F. I have 300 rounds of 75gr now.
Link Posted: 11/8/2005 3:21:41 PM EDT
[Last Edit: 11/8/2005 3:22:24 PM EDT by edwin907]

Originally Posted By Combat_Jack:
I have yet to see a test where someone uses heavy bullets in cold weather and checks to make sure they remain stabilized at a distance. Until I do, I will stick with 1/7, because I know it works.

If I get time this winter I may test it. Probably get some shots downrange in 0* F. I have 300 rounds of 75gr now.



I would be interested in seeing the results of such a test, however, I don't regularly use anything but 55, 62, and 68 grain ammo in my 1/9 barrels.
The 75 grain BH and Hornady are exclusively for my 1/7 barrels.
I just got 500 rounds of Black Hills 75 grain and I'm looking forward to trying some of it in my 1/7 shooters which are zeroed for TAP.
Link Posted: 12/27/2005 7:23:18 PM EDT
I was wondering if anyone in our colder states has tried 77gr SMK's out with 1:9 twist over Christmas vacation?
Link Posted: 12/27/2005 7:34:19 PM EDT
Holy shiet muslims!!!! I didn't know so many people "DIDN'T" have problems shooting the heavy stuff with their 1/9's. Out to 600 yards, wow. I thought it was more of a rarity that a 1/9 would stabalize. This is good to know. Thanks guys.
Link Posted: 12/27/2005 8:33:08 PM EDT
The 1/9 will shoot 69 gn. very well. But you really want a 1/7 for 75 to 77 gn. loads.

Tack
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