1:7 or 1:8 Twist?? - Page 1

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Posted: 10/7/2014 1:58:33 PM EDT

I am going to order a new barrel for my HB AR. Currently run a 1-9 from 20 years ago. It weighs about 4.5 pounds! I am getting older and want something more like 3 - 3.5 pounds total for an 18-20 inch.

Lothar Walthar has a nice Match Varmit profile in that range with 1-8 Wylde.

Reading the thread on the new BH 77 grain Tipped MK has given me pause about ordering the 1-8.

I will be running 53 grain Vmax bullets for coyote and heavier bullets for 600 - 1000 yard competition out of the same rifle. the Vmax is fairly long for weight and does require a 1-9 or faster. I currently shoot 75 grain T-1 Hornadys at 2850 - 2900 fps for long range stages but that might change if the Tipped MK becomes available!

Advice appreciated.
.

Posted: 10/7/2014 2:41:01 PM EDT

[#1]

1/7 will handle anything you can load in a magazine.

Posted: 10/7/2014 3:07:28 PM EDT

[#2]

I know a precision bullet can withstand the extra rotational velocity without accueracy suffering but when I ran an A2 it seemed the 1-7 grouped different bullet weights and makes in widely different point sof impact. 1-9 did not have that problem w everything going into 2 inches or less at 100 yd.

Anyone else had that problem?

Posted: 10/7/2014 9:55:31 PM EDT

[#3]

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1/7 will handle anything you can load in a magazine.

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1/8 will do the same minus the M196 (tracer).

Posted: 10/7/2014 10:05:39 PM EDT

[#4]

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Quoted:

1/8 will do the same minus the M196 (tracer).

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Quoted:

Quoted:
1/7 will handle anything you can load in a magazine.

1/8 will do the same minus the M196 (tracer).

M856 is the heavier tracer you're thinking of, M196 works in 1/12.

I would be wary of the 70 TSX in a shorter 1/8 or in very cold weather.

Posted: 10/7/2014 11:27:14 PM EDT

[#5]

i've always understood that 1:8 is the most universal twist rate

Posted: 10/8/2014 8:34:36 AM EDT

[#6]

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i've always understood that 1:8 is the most universal twist rate

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In my limited experience, 1:7 will stabalize heavier(longer) bullets like the 80s and up which 1:8 might not. However, for most shooters 77gr is as heavy(long) as you we will shoot. 1:8 stabalizes 77gr's just fine and from "my" barrels 1:8 shoots tighter groups with 50gr and 55gr bulk vs my 1:7.

Posted: 10/8/2014 2:00:19 PM EDT

[#7]

OP,
When you get past 500yds. with the .223/5.56MM, it is all about basic marksmanship & cheating the wind/reducing bullet drag. Long heavy bullets with high BC are the ticket. Up until the magazine length BHA 77gr. Sierra TMK cartridge, we would mostly be talking about over-mag-length loadings for LR use. I use a full heavy fluted 18" SS 1x7.7 Krieger with Frank White/CLE Match 5.56MM chamber purpose built for firing the 77gr. SMK OTM based BHA MK 262 MOD 1 loading or equivalent handload. It has worked very well. Luckily, it also shoots the 2.390" COAL over-mag-length 80gr. VLD load very well. But it will not stabilize the ultra-long 90gr. VLD with .551 G1 BC as that bullet requires 1x7 twist minimum. Minimum twist for the 80gr. VLD is 1x8 but minimum may or may not be optimum. On paper, the 18" 1x7.7 barrel I use will keep a 5.56MM NATO pressure over-mag-length 80gr. VLD load supersonic to 1000yds but just barely. Testing so far has shown that the 80gr. VLD load is accurate out to 750yds. but I will need to install a 20 MOA base for shooting past that: http://forum.snipershide.com/snipers-hide-semi-auto-rifles/273061-douglas-criterion-compass-lake.html. I use an 18" because I am married to suppressor use. My ears are getting older and suppressor use definitely keeps my neighbors happy. If you are not firing suppressed, by all means go with a barrel longer than 18" for LR use. In the past, I fired an unsuppressed 24" varmint weight barrel and it had a great MV advantage over the 18". No surprise there.

Given what I know now, my next premium barrel will be a 1x7. The 70gr. TSX bullet appears to group best with 1x7 twist and I may even give the 90gr. VLD a spin. That .551 G1 BC for the 90gr. VLD bullet looks very attractive for LR use. Good luck.

M856 tracer shown for bullet length reference only:

Posted: 10/9/2014 12:56:38 PM EDT

[#8]

LEID,

That is a great visual aid.

I will not be single loading the AR.

I would rather have the 53 VMAX regulate with my 62, 64 and 77 grain bullets than stabilize the 80-90 grainers.

Given that, would you go with the 1-8 or 1-7?

PS I have had good luck at 700 - 1000 with fast 75 grain T1 Hornady BTHP. You can get 2850 fps w BLC-2 and 2900 fps with CFE223 in a 20 inch 1-9. Not as accurate at 600 as RL15 at 2700 fps but they will usually hold on a 24 inch gong at 1000.

Interesting article by Bryran Litz on effect of rotational velocity on BC. http://forum.nosler.com/viewtopic.php?f=4&t=28357

Thanks for your advice.

Posted: 10/9/2014 1:34:50 PM EDT

[#9]

The 1x8 should definite stabilize the bullets you list for intended use all the way up to the 77gr. TMK. I went with 1x7.7 on my last barrel because I deemed it optimum for the 77gr. SMK OTM. But with the 77gr. TMK bullet being slightly longer than that, I believe a 1x7 may prove to be optimum for its use. I would definitely hold off on twist selection until we get some actual accuracy test results back on the 5.56MM TMK loading. At present, the TMK bullet's preferences are still a bit of an unknown to us. I held a 5.50" group at 750yds. with the over-mag-length 80gr. VLD in predictable wind conditions. The 80gr. VLD target shown on the other site was fired with up to 2 minutes right windage on the scope (approx. 15" bullet drift at 750yds). Because of the high BC, the 80gr. VLD bullet is very forgiving on small errors in wind call, much more forgiving than the 77gr. SMK OTM bullet. Am hoping to see pretty much the same thing with the mag-length factory BHA TMK loading. Future testing will tell the story.

On the 75gr. Hornady: The 24" 1x9 barrel I used 15 years back would stabilize and was extremely accurate with a 5.56MM 77gr. SMK OTM load. But apparently the same 1x9 barrel would barely stabilize the 5.56MM 75gr. Hornady TAP load so accuracy suffered greatly. This leads me to believe the 75gr. Hornady may prefer a faster twist such as a 1x8 or perhaps even a 1x7. After initial accuracy testing years ago, I standardized on 77gr. SMK use so there was no reason for further testing with the 75gr. bullet. BHA went with the 77gr. SMK OTM bullet for the DOD MK 262 MOD 0/1 AA53 loading over several other bullets based on a slight accuracy advantage: http://www.shootingtimes.com/ammo/special-forces-to-civilians-black-hills-mk-262-mod-1-review/

Posted: 10/9/2014 2:15:08 PM EDT

[#10]

Quote History

Quoted:
OP,
When you get past 500yds. with the .223/5.56MM, it is all about basic marksmanship & cheating the wind/reducing bullet drag. Long heavy bullets with high BC are the ticket. Up until the magazine length BHA 77gr. Sierra TMK cartridge, we would mostly be talking about over-mag-length loadings for LR use. I use a full heavy fluted 18" SS 1x7.7 Krieger with Frank White/CLE Match 5.56MM chamber purpose built for firing the 77gr. SMK OTM based BHA MK 262 MOD 1 loading or equivalent handload. It has worked very well. Luckily, it also shoots the 2.390" COAL over-mag-length 80gr. VLD load very well. But it will not stabilize the ultra-long 90gr. VLD with .551 G1 BC as that bullet requires 1x7 twist minimum. Minimum twist for the 80gr. VLD is 1x8 but minimum may or may not be optimum. On paper, the 18" 1x7.7 barrel I use will keep a 5.56MM NATO pressure over-mag-length 80gr. VLD load supersonic to 1000yds but just barely. Testing so far has shown that the 80gr. VLD load is accurate out to 750yds. but I will need to install a 20 MOA base for shooting past that: http://forum.snipershide.com/snipers-hide-semi-auto-rifles/273061-douglas-criterion-compass-lake.html. I use an 18" because I am married to suppressor use. My ears are getting older and suppressor use definitely keeps my neighbors happy. If you are not firing suppressed, by all means go with a barrel longer than 18" for LR use. In the past, I fired an unsuppressed 24" varmint weight barrel and it had a great MV advantage over the 18". No surprise there.

Given what I know now, my next premium barrel will be a 1x7. The 70gr. TSX bullet appears to group best with 1x7 twist and I may even give the 90gr. VLD a spin. That .551 G1 BC for the 90gr. VLD bullet looks very attractive for LR use. Good luck.

M856 tracer shown for bullet length reference only:

<a href="http://s9.photobucket.com/user/leid/media/Ammo/057ebfb8-54f6-4742-86a9-dbb285b1cab1_zpsfa95a404.jpg.html" target="_blank">http://i9.photobucket.com/albums/a72/leid/Ammo/057ebfb8-54f6-4742-86a9-dbb285b1cab1_zpsfa95a404.jpg</a>

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Very well written and spot-on! I shot competitively at the national level as a member of the Air Force Rifle Team for six years and have extensive experience shooting 5.56/.223 out to 1000yds. Go with the 1/8. Both will stabilize the heavier bullet, but the 1/7 is hit-or-miss with the lighter (52gr - 55gr) bullets. My current 1000 yrd rifle has a 1/8 twist and I love it!

Posted: 10/9/2014 2:51:58 PM EDT

[#11]

Howdy "Shooter",
Very good to have someone with experience chime in. I am nothing more than a motivated novice at LR shooting with the 5.56MM so am always willing to learn more. 1st match with the AR15/M16 was in '79. I placed 3rd firing a .223 pressure Speer 70gr. semi-spritzer over H335 handload against my fellow M14NM shooters. They thought it was a joke when I left my Glenn Nelson built M14NM in the rack that day. What 5.56MM loadings did/do you normally use for 1000yd. competition? BHA 77gr. SMK AMU, BHA "Long Throat" 80gr. SMK, Atlantic Arms 77gr. SMK AMU, in-house custom?

TIA!

Posted: 10/9/2014 5:02:22 PM EDT

[#12]

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Quoted:
Howdy "Shooter",
Very good to have someone with experience chime in. I am nothing more than a motivated novice at LR shooting with the 5.56MM so am always willing to learn more. 1st match with the AR15/M16 was in '79. I placed 3rd firing a .223 pressure Speer 70gr. semi-spritzer over H335 handload against my fellow M14NM shooters. They thought it was a joke when I left my Glenn Nelson built M14NM in the rack that day. What 5.56MM loadings did/do you normally use for 1000yd. competition? BHA 77gr. SMK AMU, BHA "Long Throat" 80gr. SMK, Atlantic Arms 77gr. SMK AMU, in-house custom?

TIA!

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Leid,
I normally shot team provided ammo (Mk262 Mod1) back to 600 and 80gr hand loads back to 1000. I started shooting the M14 service rifle (SR) at 1000 (M118 LR), but when I moved to match rifle (MR), I shot my White Oak AR. Now, I shoot exclusively AR's at 1000. Both my service rifle and my match rifle have White Oak uppers. For several years we were provided Black Hills AMU ammo loaded with 80gr SMK's. When those ran out, I started loading with 80gr SMK's and 80gr Berger VLD's. The Bergers have a better ballistic coefficient, but they seemed more sensitive to seating depth. When I loaded the Sierras, they were the same length for both MR and SR. The Bergers I had to seat to the individual rifle. Currently, I load 80gr Sierras with 24.5gr Varget for 1000yds. Although I never competed with 77gr Sierras at 1000, there were a few guys on our team that didn't reload and shot well (185 or 190 out of 200) with the Mk262 Mod1 (77gr SMK's) back to 1000.

To keep this on topic, most of our team shot Krieger 1/7.7 barrels. I'm not a big believer that you need a Krieger to win. I shot High Master scores and made the President's Hundred with a RRA 1/8 Wilson barrel.

Posted: 10/9/2014 7:22:07 PM EDT

[#13]

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1/8 will do the same minus the M196 (tracer).

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1/7 will handle anything you can load in a magazine.

1/8 will do the same minus the M196 (tracer).

This! My Savage bolt rifle is quite accurate with 77 SMKs and it's 1-9 twist. I've had good results with 75 grain Hornadys in a couple 1-9 guns including a Sig 556. I've yet to have any issue with 1-8 AR barrels.

Posted: 10/9/2014 9:36:16 PM EDT

[#14]

Thank you guys!

LEID you may have had trouble w the T2 bullet. I have been shooting the T1 as a reload. Higher BC and for some reason it does stablize in my 1-9 even at 2700 fps or less. I began to increase velocity when Hornady published NATO pressure data just to increase fragmentation range on coyotes but found it helped get it past 700 yards.

Since the 77 TMK is probably the longest bullet I will shoot will probably go w 1-8. I am sure extra rotational velocity will help 77 TMK achieve maximum BC but I use the same rifle for coyotes at 200 yards w lighter bullets and will probably give up the X ring for convenience. I am more of a casual local tactical match shooter than a national class shooter like you guys!!!!

I have a freind who is going to use a 1:6.5 barrel for the TMK. Let us know how the TMK flies from your 1:8 and 1:7 please!

I will do the same.