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Author Topic: Bullet weight clarification  (Read 5911 times)

garand4life

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Bullet weight clarification
« on: October 21, 2009, 06:40:01 PM »
I have an AR15 with a barrel twist of 1/9. I also have quite a stock pile of 75grain Hornady TAPFPD .223. Will the 1/9 twist stabalize this heavier round sufficiently to maintain a 50-100 yd effective range or will this thing fly off the handle?
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sanjuancb

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Re: Bullet weight clarification
« Reply #1 on: October 21, 2009, 07:11:58 PM »
From 6mmBR.com

Twist Rates
223 Rem Remington barrel Twist rateThe .223 Rem shoots a wide range of bullets very effectively, from 35gr flat-based varmint bullets, to ultra-long 90gr VLDs. However, you'll need the right twist rate for your choice of bullet. For max velocity and accuracy with the lightest bullets, a 1:14" twist may be ideal. More versatile is a 1:12" twist that will allow you to shoot the popular 60-64 grain match bullets. (However, a 1:9" twist is needed for the steel-core 62gr bullet used in the M855 military loads, because that bullet is as long as most 70-grainers.) For normal lead-core jacketed bullets, a 1:9" twist will let you shoot up to 73gr bullets. Since most .223 Rem shooters prefer bullets in the 50-73gr range, a good "do-it-all" solution is a 9-twist, unless you're a Highpower competitor.

For long-range match purposes, long, high-BC bullets are favored for their ability to buck the wind. You'll want at least a 1:8" twist to shoot the 77gr and 80gr MatchKings and 80gr Bergers. To shoot the new 90gr pills, a 1:6.5" is recommended, though a true 1:7" will work in most conditions.

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.

Barrel Twist Rate   1:14"   1:12"   1:9"   1:8"   1:7" or 1:6.5"
Max Bullet Weight   55gr FB   65gr FB   73gr BT   80gr BT   90gr BT VLD

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garand4life

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Re: Bullet weight clarification
« Reply #2 on: October 21, 2009, 07:46:01 PM »
So..... that's a maybe?
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billt

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Re: Bullet weight clarification
« Reply #3 on: October 21, 2009, 08:04:04 PM »
The 75 Grain Wolf .223 load was found to be quite accurate in a 1 in 9" twist barreled AR-15.  Bill T.
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tombogan03884

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Re: Bullet weight clarification
« Reply #4 on: October 21, 2009, 08:13:29 PM »
 Sounds like what you have (1:9) is "good enough" for what you want, but to get the most out of your rifle you would be better off with a 1:8.
Judging by the ranges you mentioned (50 - 100 yards ) you are not planning on shooting Bulls eye competitions with it, 1:9 should be fine.
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Re: Bullet weight clarification
« Reply #5 on: Today at 04:30:24 PM »
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DonWorsham

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Re: Bullet weight clarification
« Reply #5 on: October 21, 2009, 08:19:30 PM »

Quote from: sanjuancb on October 21, 2009, 07:11:58 PM
From 6mmBR.com

Twist Rates
 We'd only select a 1:7" or faster twist barrel if we had a need to shoot the 90gr VLDs.

Barrel Twist Rate   1:14"   1:12"   1:9"   1:8"   1:7" or 1:6.5"
Max Bullet Weight   55gr FB   65gr FB   73gr BT   80gr BT   90gr BT VLD

What is the twist rate of the M16?
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MikeBjerum

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Re: Bullet weight clarification
« Reply #6 on: October 21, 2009, 08:31:38 PM »
Garand4life,

My understanding from talking to a friend that does 100-600 yards with .223 is that 1 in 9 will stabilize anything for under 200 yards just fine.  He, and many of his fellow shooters, are using between 1 in 7 and 1 in 8, he is using 1 in 7.75, for 75 to 90 grain.

He instructed me that at a hundred yards you can get by with a lot if you are not trying for one hole groups.  Fox and Coyote have a large enough kill zone to be very forgiving.  When you go for more precision it is a total load and gun package.  Work up loads considering bullet weight, bullet speed and head space (oal).

Bottom line, for 75 grain in a standard 1 in 9, I'd load and shoot 'em.  If you keep the speed down in a standard range they should do just fine.
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1911 Junkie

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Re: Bullet weight clarification
« Reply #7 on: October 21, 2009, 08:39:41 PM »
I loaded 75 gr BTHP to shoot out of my 24" AR (1:9 twist). They were insanely accurate. I just loaded up some different rounds in 1/2gr increments and stuck with the tightest group. I could easily keep a 30rd mag in nickle sized group at 100yds.
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Big Frank

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Re: Bullet weight clarification
« Reply #8 on: October 21, 2009, 08:52:21 PM »
Quote from: DonWorsham on October 21, 2009, 08:19:30 PM
What is the twist rate of the M16?


1:7. They need an extra fast twist to stabilize tracers because the bullets are so long. 1:9 is good for everthing except tracers.
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twyacht

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Re: Bullet weight clarification
« Reply #9 on: October 21, 2009, 09:14:40 PM »
At moderate ranges, a 1 in 9 is great. Zombies will never know the difference.

With a bipod, my Sig556, 1in 9, 16" Barrel, can keep a softball size group at 100 yds. Through 62gr rounds.

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