OK, I have a Dan Lilja 16" SS barrel in one of my ARs. It is a precision, high-end barrel and it is very nice. It will put rounds on top of each other at 100yds if the shooter is up to it. It is also very expensive.
Here is the problem though... with the very best shooters I can find behind it (not me), match ammo, better optics, and shooting from a bench, the barrel is a few tenths of an inch tighter at 100yds than what an RRA SS match barrel will produce. I've shot the Mike Rock SS match barrels and they are the same deal - great barrels with beautiful precision; but it is a lot of money for those few extra 0.1" changes.
At 600yds, even if you double the amount of difference I saw and then multiply it by six, you are talking about a difference of a couple of inches and you will definitely be paying more than $150 for each of those inches.
If you are doing practical shooting, then the differences just evaporate because you will rarely be able to assume a stable enough position to appreciate the differences. Given all that, I really think it is tough to beat just your plain jane RRA SS match barrel with a Wylde chamber - or even a nice quality chrome-lined barrel.
On twist, I would really recommend 1:8 or 1:7. You will still be able to shoot 55gr and 62gr just fine; but you'll have the option if you want it. At 18" with a good match barrel, you will still probably be able to shoot the heavy stuff with a 1:9; but you'll be right on the edge of stability and may lose that ability with big temperature drops or as the barrel gets a bunch of rounds through it.
speaking of fluted barrels, should i go with a heavy fluted barrel or just a heavy barrel, what real advantages will i have with getting a fluted barrel?
The advantages of a fluted barrel are that it is a bit lighter; but we are talking a few ounces at best
i forsee that the spr upper will not be shot that much maybe 300-500rds a year, my 16" upper will see more use than that like 1000rds plus a year. i don't plan on shooting the spr at high rates of speed just slow accurate fire at longer ranges so the barrel getting heated shouldn't be a big issue for this particular upper.
Any AR15 barrel you could buy will handle that kind of shooting with ease. My Lilja barrel has 2,423 rounds on it and is just shy of a year old according to my log (not much time to shoot this past year). Check some of Zak Smith's 3-gun competition reports for an idea of what you can do even with a SS barrel (and an SS barrel will not handle heat as well as a chrome-moly or chrome-moly-vanadium barrel).
