hello, been a long time since i posted here, in fact so long that the 18" was mostly for the 6.8 round.  anyway, i have been seeing the 18" 1/8 in 5.56 lately.  is this just for shooting @ 600+yds?

anybody?

Quoted: Hello, been a long time since I posted here, in fact so long that the 18" was mostly for the 6.8 round.  anyway, I have been seeing the 18" 1/8 in 5.56 lately.  Is this just for shooting @ 600+yds?

Not necessarily 600+ yards..., but most defiantly 60+ grain bullets!!

1:8 twist should be able to stabilize bullets up to .941" in length.

The 18" barrel will produce approx. 60 FPS more velocity than the 16"  

Generally 2" of barrel will have no discernable effect on accuracy.., everything else being the same.., unless of course the particular bullet you are useing is effected one way or another by 60 fps, which is of course a possibility. There are so many varibles involved that a person really needs to do their homework, as you seem to be doing, and then after your make your choice on hardwareyou'll need to spend some time finding the best ammo for your rig. For handloaders this is a task to look forward to (that's why we handload), but for Factory load shooters this can be somewhat of a hassle not to mention expensive!  It 's  pretty much a "Hit & miss" either way" (pardon the pun) but well worth the effort when you find the load that is "one" with you & your set up!!