AR15 bullet weight vs barrel twist

me ^ | 11-28-2008 | Wobbly Bob

[WOBBLY BOB]

what's the best barrel/bullet weight combo?

IIRC, 62 grain 5.56 is best in a 1:9 barrel.

[WOBBLY BOB]

thanks for your comments and inevitable smart remarks.

keep your head down in Walmart.

[waterhill]

Barrel length is a factor as well.

Do you want to shoot a pecan out of a spuirrels paws at 200yds? Do you want to scramble an oinkers brain at 50yds?

[WOBBLY BOB]

Only if the pecan is armed and threatening, so yes, that would be good. I have a 20” barrel.

[wastoute]

1:7.75 is required to stabilize the 80 grain bullets

[Mad Dawg]

Okay, I'm new at this. What's optimal for a 16" at 1 in 7 — and where do yhou go to get this info?

[waterhill]

Its all in what you are comfortable with really. My EBR is 16” @1-9 and I don’t think I have ever used anything bigger than 55gr. I hunt varmints and wild bacon with mine.

[USMCPOP]

Check this thread, and especially the third post down.

http://www.thehighroad.org/archive/index.php/t-158429.html

Les Baer and Wilson Combat AR rifles offer 1 in 9 as a standard.

Then there’s this info: http://www.shilen.com/calibersAndTwists.html

Also see http://www.triplebreakproducts.com/FAQ/twist_rate_for_barrel.htm. (Wobbly Bob - see the comment about the 1:14 twist in this link. Maybe that’s what you want, LOL.)

[The KG9 Kid]

I personally recommend 1x9 twist to everyone and forget about it. That’s regardless of barrel length, muzzle velocity, or bullet fragmentation dynamics. This advice would only change if we’re dealing with very short barrels where a suppressor is mounted.

[jim-x]

Here’s another link with information on AR15 ammunition. Twist rates are discussed under “Performance...”

http://ammo.ar15.com/ammo/

[Kirkwood]

I don’t know enough about this topic, but doesn’t it depend a great deal on the coefficient of friction of the bullet material (casing) which determines how well the barrel is able to grab and spin the bullet? It is not simply grain weight and twist rate. It is also the material properties, the barrel length, how clean or dirty the barrel is, and probably several other factors.

[Uri’el-2012]

1 in 7 in .223 in a Savage 12/110

Model 12 Long Range Precision Varminter– with AccuTrigger™

[joseph20]

If you are interested in a serious discussion, then visit these forums:

http://www.ar15.com/forums/forum.html?b=3&f=118

http://www.m4carbine.net/forumdisplay.php?f=3

For example, this wonderful gem of 100% truth can be found here:

Another common misconception is that bullet weight determines the optimal rifling twist. This is incorrect in that it is actually bullet (projectile) length that should be used to determine the twist rate. Generally speaking, however, the heavier bullets are also longer so while technically incorrect it is common to say that a 1:7 twist is more desirable for the heavier 75 and 77 grain projectiles. Therefore, choosing a barrel twist really comes down to first choosing your projectile weight, and more correctly, length. If you work for a department that mandates or issues a certain ammunition then this should be your guide when choosing a rifling twist rate. A good rule of thumb is that 1:9 will stabilize bullets in the 45 to 62 grain range, and 1:7 will stabilize bullets in the 55 to 77 grain range. Like all things this is not a given, and any barrel should be tested with the intended ammunition to ensure the desired results are achieved.

[USMCPOP]

Personally, I’d prefer a barrel that’s between 6mm and 7.62mm :)

But seriously, ballistics is a very complex matter and results do vary. Good post.

[PubliusMM]

My 20” 1:9 is doing just fine out to about 250 yds on varmints, using 55gr ammo. Coyotes closer than 150 yds good on the same stuff.

Good luck...and, remember...good sight picture, breath control, and squeeze smoothly.

[Buffalo Head]

Select the bullet first and the twist rate to stabilize that bullet. Google "Greenhill Formula" for details on how to calculate the necessary twist rate for a particular bullet.

Too slow a twist with produce an unstable bullet and poor accuracy.

Too fast a twist is detrimental to accuracy.

A 1:9" or 1:10" twist will stabilize all common bullets less than 64 grains in weight, without degrading accuracy. Faster twists and heavier bullets in the .223 Rem / 5.56mm are a solution to a problem that doesn't exist. If you need longer range or better terminal performance, use a rifle chambered for a larger cartridge.

[wastoute]

shooting 80 gr Sierras is an option that is available and has applications. 600 yd slow fire prone is one. I have fired my spacegun with these bullets at 1000 yds and the rifle/bullet combo performed well. The barrel is 26 inch SS with 1:7.75. At 1000 yds all my rounds were still supersonic.

[mpstan]

I don’t know if I can resurrect this thread, but I had a related question...... I’m researching AR 15s for the same reason most here are.... personal and home defense if things go to “mad max”, and becuase I’m afraid that if I wait much longer I won’t be able to get one.

Never owned one; right now I own a 12ga shotgun, 2 .270 deer rifles, and my favorite, a 6.5x55 Swede chambered Tikka deer rifle.

Because of my last selection, I started hand-loading. As far as AR-15s go, I’m thinking about the newer 6.8mm version, which should have better stopping power than a 5.56 but less recoil than an AR-10 with a .308.

If I’m not afraid to handload, are there other negatives to considering the 6.8mm? What do you think?

Thanks!