loose is the way the US military sets them up for use, also absolutely neecessary for match shooting.
what is almost as important is to have a strong clamping action between the triggerguard assembly and the stock of the rifle. My own is shimmed with a strip along each side taken from a (shock!) cigarette pack. Works just fine.
if the gas cylinder assembly gets loose, as it will from time to time, you can remove it and slightly (accent SLIGHTLY) pein the splines on the barrel, then tap the gas cylinder back almost to its final position, use the gas cylinder lock to get it to its final position. do it like this and it should shoot.
forget fancy sights...... just put the back sight out 2 clicks (the front sight is 4 minutes wide) and aim with the CORNER of the sight.
My own rifle is set up like this and it will shoot half a minute if you can hold it, sandbags of course.
most important of all: have fun.