Any rifle can be a sniper rifle...its the man behind the rifle that makes the difference.
I quickly grew tired of a couple of "sniper forums", there are a few genuine guys there...but most are all about letting the equipment do the work. A good rifle is helpful, but a good sniper can make it happen with any decent rifle.
Carlos Hathcock's rifle was tested after his retirement...it shot 2 MOA.
I've got a couple of custom rifles, and what little is gained in accuracy is not worth the price of admission...the most important thing for a sniper rifle is durability because even if you guard it, protect it, baby it, etc...it still has a rough life.
Heavy barrels are useful if one was to find himself in a target rich environment...shooting fast will cause a sporter barrel to start flinging bullets in all directions when it heats up. Shooting slow...any barrel will do as long as it shoots true.
Its one thing to be sniping in a jungle (a target here and there)...but sniping in Fallujah was likely a lot like shooting prairie dogs (fast and furious)