Re: barrel twist in AR style 223
For whatever it's worth, I've had 3 different Ar-15's over the years. One had a 1-7, the last two have 1-8. I still have the last two. I think maybe I could be using 1-9 quite easily, because my most recent one seems to like the 60 grain bullets. It doesn't seem to like the 55 grain stuff I've tried. 69's and 77's shoot decent, but best accuracy has been with 60's so far........especially with factory ammo. The 1-7 was only gauranteed accurate with 69 and heavier bullets.
I am thinking you'll want to use something in the 55-69 grain loadings (based on your 2nd post). I know that some Tactical ammo is available in 55 and 68-69 loadings from more than one manufacturer. A 1-8 or even 1-9 (as Kevin said) should theoretically shoot all those just fine. I've often wondered if I should have went with 1-9.
Of the 3 I've had, the best for mobility was the shortest one (18" heavy barrel).
I would consider 20" medium weight barrel to be max for quick mobility, especially if your talking about getting it into and out of a vehicle or the vehicle window fairly quickly.........These shorter barrels probably won't shoot the heavier bullets as efficiently as the lighter ones.
Just my 2 cents.