[RDRJR]

What are the advantages/ disadvantages of the 1:7 1:8 and 1:9 rate of twist in 223 ar's. How about bullet weight to rate of twist?

 

[jbpmidas]

The faster twist, in general, stabilizes longer bullets better. Usually longer means heavier. I got my AR barrel in 1:7 to ensure it would shoot heavier bullets. Mine does very well with 69 grain Nosler CCHP's. It will shoot 10 well under 2" at 200 yards. 1:9 is generally in the middle and should shoot 69's and 55's pretty well.

 

[RDRJR]

Thanks, My 20" has a 1:7 my 10.5" has a 1:9 am leaning toward a 1:7 for my 16" M4 style build.

 

[miker84]

The faster twist, in general, stabilizes longer bullets better. Usually longer means heavier. I got my AR barrel in 1:7 to ensure it would shoot heavier bullets. Mine does very well with 69 grain Nosler CCHP's. It will shoot 10 well under 2" at 200 yards. 1:9 is generally in the middle and should shoot 69's and 55's pretty well.

That pretty much sums it up. The length/style of the bullet comes into play along with the weight.

This chart was sent to me a while back, maybe it well help.
.223/ 5.56mm
1:16 up to 55 grains
1:15 up to 55 grains
1:14 up to 55 grains
1:12 35 – 63 grains
1:9 45 – 69 grains
1:8 55 - 75 grains
1:7 62 - 90 grains

 

[jbpmidas]

I'd go along with that chart, as mine does not shoot 55's well at all. That is something to take into consideration when building a new one. If you don't reload and want to shoot the "cheap" stuff, you need to go with 1:9 or slower.