Topic: AR-15 Barrel Question

[WhaleNoises]

So I'm looking at building or buying my first AR-15. At this point I'm trying to learn all I can about the different manufactures, and have been told that BMC makes very good rifles. The question I have is that I've heard that when the twist rate on a barrel gets too fast that it can tear apart smaller bullets. I found that a 1 in 9 twist seams to be average. With BCM I can only find barrels with 1 in 7 twists. Wont that normally tear apart .223 rounds?

[9Shooter]

There's some good info here, including twist Q&A: http://razoreye.net/mirror/ammo-oracle/AR15_com_Ammo_Oracle_Mirror.htm

I can't speak authoritatively on your question but everything I've read so far says while 1 in 7 isn't ideal for 55gr bullets, it will shoot them fine.

[romo23]

from my understanding the 1/7 twist just stablizes the bigger bullets 62 and 69grain better than the standard 1/9 that is ideal for 55 gr. that being said one of my ar's has a 1/7 twist and it shoots 55 just fine and the difference in accuracy is negligible for my skills. p.s. i have always been happy with bcm.

[Grumblecakes]

my experience has been with 1/9 and 1/8 both shoot 55-75gr just fine, ive only shot 75gr bthp out of the 1/9 a few times and it was out to 100yds so i cant say if they stay stable or accurate. the 1/8 shots 75 amax and bthp amazingly they are accurate and stable out to at least 450. everything from 55-75 seemed pretty good. however the lighter bullets would never group for me. i bought 250 45grs and one point, 3 different powders and they just wouldn't work.  i never had them fly apart either i even tried just cause i wanted to see what it looked like. im guessing the jacket failure is with cheaper lighter thin jacketed bullets.

 fwiw gi issue m16a2 is 1:7 and it shoots 55 pretty accurately. guy in boot camp shot 249 out of 250 (thats center mass 49 times with one 'flyer') on the kd course (i barely made expert with 220)

[Nealio]

I run a Bravo Company 1/8 stainless:

http://www.bravocompanyusa.com/BCM-18-SPR-SS410-Barrel-with-Rifle-Length-Gas-p/bcm-recbrl%2018ss.htm

And it shoots 55 gr bullets awesome

[Jaggy13]

I run a 16" BMC 1 in 7.
I shoot 55's by the thousand....

[hessmanca]

I think the question is what is the purpose for the rifle and what kind of ammo you are going to primarily shoot out of it.
I have owned several different lengths and twists.  I currently run a 16" Noveski s/s with 1/7 twist.  I shoot 55gr fmj for training and 64gr bthp for work.  It handles both just fine and there is very little noticeable difference in accuracy.  I also have a SBR with an 11 1/2" barrel with a 1/9 twist.  It definitely likes the lighter 55gr better than the 64gr.

And before those enthusiasts out there ask... 64gr? I know it is a weird weight; however it is what I am issued at work.  They are Speer Gold Dot rounds.....

So if you are going to have a rifle to shoot as an everyday defensive carbine, I really don't think you can go wrong 1/7, 1/8, or 1/9.  The big difference you will see is the quality of barrels out there.  Bravo makes a great barrel, reliable and accurate.  If you are building a rifle for longer distance shooting I would go with 1/7 so it will handle the heavier rounds better.

If I can make one suggestion....IMHO... No matter what twist rate you go with, if you are building a 16" gun, get a mid length gas system.  You will love it compared to a carbine length.  I will never run carbine length again on a 16" or longer gun.

[ballardw]

Potential damage to a bullet is more dependent on the bullet's designed velocity. Hence you find .22 caliber bullets that are designated "for 22 Hornet". These have very thin skins as they are supposed to be used at velocities around 2,000 fps. Most of these are also in the 40 grain weight range so may be what was meant by "smaller".

Since the loads for many other modern center-fire 22s run in the 2500 to 4000+ fps the Hornet designed bullets may come apart or deform.

Tighter twists do mean more friction so lower velocities may result for the same bullet/cartridge in different rifles. The original M16 had a 1/12 twist to make it easier to meet the velocity goal and Stoner originally proposed 1/14 IIRC.
Faster twists are also an issue with cast bullets but I doubt you had those in mind.

[charlie76]

This is a pretty good info if you are building.  http://www.mapartsinc.com/anything.asp

[J Mack]

It would be easier to recommend a twist rate if you told us how you intend to use your rifle and what ammo you intend to use.
For instance most of the cheap surplus bulk ammo in .223 or 556 use the 55 gr bullets and I would use a 1:9 twist barrel with a NATO chamber if you’re building a range rifle for plinking.
If you plan on building a SHTF rifle and you are going to stock up with some kill shit 62gr to 70gr super whammy ammo I use a 1:7 twist barrel with a Match Mod 0 chamber.
The barrel twist is determined by bullet length and speed or another way to look at it is a bullet needs RPM to stabilize and a short 55gr bullet @ 3000FPS needs less twist rate than a long 70gr bullet @ 2000FPS to achieve the desired RPM.

This is a good article on the subject.  http://bulletin.accurateshooter.com/2008/06/calculating-bullet-rpm-spin-rates-and-stability/

This is the handy calculator from the article.
http://accurateshooter.net/Blog/millerformula.xls

Edit to answer your question  I'm not sure you can push a bullet hard enough with the .223 to have jacket issues with a 1:7 twist

[WhaleNoises]

I'm planningon using it for SHTF scenario or a zombie apocalypse, lol. Until then it will be plinking and target practice. Or hunting possibly if I ever do. I'm more into guns for the tacticool aspect not hunting. So I will probably shoot cheap fmj 5.56 and stock heavy killing rounds. I plan on 16" so I can change the flash suppresser if I want.

[J Mack]

I'm planningon using it for SHTF scenario or a zombie apocalypse, lol. Until then it will be plinking and target practice. Or hunting possibly if I ever do. I'm more into guns for the tacticool aspect not hunting. So I will probably shoot cheap fmj 5.56 and stock heavy killing rounds. I plan on 16" so I can change the flash suppresser if I want.

Then I would look at a 1:8 or a 1:7 twist barrel as both will work fine for plinking with 55gr ammo but both will stabilize the longer kill shit bullets better than the 1:9.
The better performing heavy Zombie killing bullets often have thicker copper jackets or entire copper construction making them longer than their typical lead/copper counterparts making them longer for a given weight necessitating a faster twist.
Not to go in to too much detail with the limiting factors of the round or the weapon system the best I get is 2780FPS with an all copper 62gr TSX bullet and I shoot these in a 1:7 barrel.

[No-One]

I personally like the 1 in 8 twist just because I believe it gives me the most options . From 50 grain V-Max to the 77 grain SMK's I pretty much have it covered .