Question on Ar-15 barrels?Is it safe to figure that trying to get good accuracy from a 223 with a 1 in 9" twist using 55 grain bullets would be an effort in frustration??

Reply:You can blame the military for this issue of twists -everybody blames us for most other things. The .223 is a military cartridge as we know. In 1968 when I was handed my first M-16, it was a 1:12 twist. Colt wanted a 1:9 twist, but the military was worried about barrel life, so 1:12. In the mid-1980's the A2 came along with the SS109 cartridge. Again, the makers said, "use a 1:9 twist." BUT, they wanted to get this cartridge out to 600 meters so 1:7 twist compliments of Quantico and the USMC. The Army also bought into it. After a few thousand barrels later, guess what the current issue and preferred twist for military NATO standard 55-64gr bullets is? 1:9.

It was a long trip around the barn
This guy claims that he is some oracle of the Ar, just wandering how close he got?

Shadow

The 1/7 twist is to stabilize M856 tracer to the full extent of its burn, it has nothing to do with M855. Armalite and later Colt designed the first AR15 with a 1/14 twist, which failed to stabilize rounds below 0 degrees Fahrenheit, so they switched to 1/12. 1/9 hasn't ever been used by the military, but was considered for the M16A2.

+1
1 in 7 spins bullets faster so you can get more stability with a longer round. As long as it doesn't spin apart a smaller bullet, it will work fine. The closest the military has ever gotten to 1 in 9 is 1 in 8 with the SPR.

Every bit of what he said was wrong.  The experimental M249 (when it was being evaluated as a possible SAW) started out with a 1/9 twist but the tracer was changed so the 1/7 was made for that.  It has nothing to do with barrel life or M855 ammo.  We did have a 1:12 but as stated it started out 1:14 not 1:12.  There are no 1/9 barrels used in the military certainly not standard issue and there are no 64 or 55 graim NATO rounds.  The only NATO 5.56mm round is 62 grains.  Complete ass-hat IMO.

You fellers just made my day
Shadow

Quoted: +1 1 in 7 spins bullets faster so you can get more stability with a longer round. As long as it doesn't spin apart a smaller bullet, it will work fine. The closest the military has ever gotten to 1 in 9 is 1 in 8 with the SPR.

I thought the SPRs were 1/7.

Nope.  This article says 1/8.  United States Navy Mark 12 Mod 0 Special Purpose Rifle (SPR)

Why are all the aftermarket and clones being built with 1/7?

Quoted: Quoted: +1 1 in 7 spins bullets faster so you can get more stability with a longer round. As long as it doesn't spin apart a smaller bullet, it will work fine. The closest the military has ever gotten to 1 in 9 is 1 in 8 with the SPR. I thought the SPRs were 1/7.www.websmileys.com/sm/sad/533.gif Nope.  This article says 1/8.  United States Navy Mark 12 Mod 0 Special Purpose Rifle (SPR) Why are all the aftermarket and clones being built with 1/7?

They are not... MSTN build SPR clones use 1/8 stainless barrels.

FWIW

I can get MOA @100 yards out of my Bushy chrome lined M4 bbl with Win SuperX 55gr PSP.

1/9 is good for 45gr to 68gr with exceptions.
55gr or 62gr is about perfect for 1/9 twist.

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