Beckman - that is pretty good insight on the op-rod dwell time/action issues, and certainly helped my understanding, though Molon's right about that being outside the scope of this argument.
To squeeze out maximum accuracy at 100yd, might as well run a heavy 16" and drop the gas system altogether - but it sounds like you have an opportunity to take it out to 600+ meters - In which case a 16" or 18" (in middy, intermediate, or in the case of the 18 even rifle length gas system). While you can get more than adequate consistency out of a 10" barrel, velocity will make the biggest difference, hence why longer barrels. Between otherwise like barrels, at 100m there's no difference between a 16" and 18".
[ETA] Jmart did a better job explaining this...
You can hit 18" targets at 500m with a rack grade M4 barrel using good ammunition, and that's not even floated. You should be able to easily maintain MOA accuracy out to half a click with a floated 16" barrel using match/HPBT ammo, With an 18 or 20" and an adequate pile of practice ammunition, hits on 18" steel is doable beyond 600m, for sure; just be prepared to spend a bit more on ammunition for the good stuff out there.
Good 3-9x or 2.5-10x glass will be a big part, so find one you like and a mount that works, and you'll be set there. NF 2.5-10x would be great, or if money's tight, the new Vortex PST 2.5-10x (it's very large/heavy, but the larger objective isn't bad for range only use). I personally run a Leupold Mk4 2.5-8x36mm ITMR unit on an 18", and I've been pretty happy with it.
I'd say any medium or thicker contoured SS barrel, properly floated will give you the results you're after - 16" or 18" will do, and gas system won't be that relevant. Any quality barrel with a good BCG in spec, with good ammunition will cycle just fine. A Noveske or GTS Operator will get that done with a 5.56 chamber, and any of the high end (Douglas, Krieger, CLE, WOA) options with slightly tighter chambers will probably yield great results. Handloading (75 and 77gr OTM bullets) stands to give you even better results, though digging through Molon's prolific and informative posts will be a huge help here - Hornady and BlackHills seem to be perennial favorites.
If you're looking at opening up the old budget, I'd just go ahead and pick up a high end SS barrel, go a bit over budget on the optic and mount; get a top end trigger (Jewell, Wilson TTU, Timney, or a Geisselle) and start looking at either reloading, or getting top end match rounds. There's a multitude of great options, and staying MOA with match ammunition is quite do-able.
Last edited by TehLlama; 06-01-10 at 17:14.
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