# 55GR - 75GR .223??? 1/9 or 1/7



## Kyle1337 (Mar 22, 2008)

I've been told different things about this, but is it okay to use 55grain .223 ammo in a 1/9 twist barrel, I was told not to use anything less than 62GR .223s unless its a 1/7 twist. Any clarification would be helpful. I'm not sure if this would be in the wrong thread, sorry if it is.


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## BOSS302 (Mar 25, 2008)

It's the exact opposite. 55gr works great with a 1/9 twist, it's the higher weights that tend to have problems. A 1/9 twist barrel will usually cause a 75gr bullet to more or less tumble through the air, instead of pierce through it. It all depends on the build tolerances of the barrel you are using. Tigher barrels will be more effective w/ higher weight loads as will one with a 1/7 twist.


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## DJ Niner (Oct 3, 2006)

Kyle1337 said:


> I've been told different things about this, but is it okay to use 55grain .223 ammo in a 1/9 twist barrel, I was told not to use anything less than 62GR .223s unless its a 1/7 twist. Any clarification would be helpful. I'm not sure if this would be in the wrong thread, sorry if it is.


1/7 = fast twist (in .223/5.56mm; current military weapon twist rate)
1/9 = medium twist (for commercial use, intended as a compromise)
1/12 = slow twist (original M16/M16A1 twist rate)

1/7 will shoot everything (from about 40 grains through 77 grains) safely, but accuracy might be poor with 55 gr and lighter bullets. Lightly-jacketed 40 grain varmint bullets in very high-velocity loads have been known to come apart in flight on occasion (nothing gets to the target) when fired in a 1/7 barrel with a rough or heavily fouled bore.

1/9 will shoot most COMMON bullet weights (55gr - 69gr) with good-to-excellent accuracy, and should handle almost every bullet weight safely. It's a good compromise for most users, and as such, it is offered as a standard twist rate in most AR-style rifles. Really heavy or really light bullets may not work well (or stabilize at all) in this twist, but that should be considered an accuracy, not a safety, problem.

1/12 is rarely encountered in AR-style rifles/carbines nowadays, unless it is a retro-style triangular-handguard early AR. It was designed to work well with 55 grain bullets, and in most cases will shoot 40gr - 60 grain bullets with good (or better) accuracy. It will not stabilize heavier bullets (above 60 grains) except under certain circumstances, and even then the bullet may rapidly destabilize soon after firing. 1/12 is probably the most popular of several twist rates used in bolt-action varmint rifles in this caliber.

Other .223/5.56mm twist rates are available in certain weapons (1/8 for heavier-bullet-but-not-the-heaviest-bullets target loads; 1/10 for older Ruger Mini-14s and some bolt-action varmint rifles, etc.).

Exceptions may be found for all of these statements, but they will generally hold true under most circumstances and conditions.

Read the following (all of it) and it should answer many or all of your questions:
http://ammo.ar15.com/


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## Baldy (Jun 21, 2006)

Thanks there Mr DJ for the info. It answered a few questions I had on these rifles. :supz:


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## Anarius (Mar 8, 2008)

Good info, just one thing to add. Service M16s (20") have a 1/9 twist I believe. The M4 does have the 1/7.

55gr is as light as I shoot out of a 1/9. 62gr (mil spec M855) ammo is great, but hard to find unless you buy surplus which is ever harder to find and not that great an idea in a .223 civilian rifle. My compromise is 60gr. Works great.

That said, 55gr will go 'boom' and then preceed downrange.


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## Mike Barham (Mar 30, 2006)

The M4, M16A2 and M16A4 are all 1/7. The M16 and M16A1 are 1/12.


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## Kyle1337 (Mar 22, 2008)

Thanks guys (or girls) for the clarification, I really appreciate it. For some reason they never taught us this in the Army, they taught us how to aim and shoot respectfully. I just bought an AR/M4gery M&P15 with a 1/9 I bought it cause it stated it was "mil-spec" (lies) the M4 I trained on was 1/7 which is what I was looking for. Lesson learned. Verify mil-spec first yourself before taking their word for it. I'm not sure what a big deal a 1/7 vs 1/9 would make, but I'd like to get as close as to the M4 I was trained on as possible without buying that specific colt I had for 1700+ dollars and getting an SBR agreement from our lovely chief of police.


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## Mike Barham (Mar 30, 2006)

Actually, 1/9 is a better choice unless you are only shooting current military ammo. 1/7 is pretty limiting.


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