What if the barrel is loose do it need to be tighten?
The LasserMax Rod is non-adjustable, and is intended to be used as "point and shoot" device.
As such is not a very accurate lasser, and the point of impact may drift after each shot depending on the gun.
I do not understand the "barrel loose" portion of the question, on a SIG gun has no adjustments to tighten the barrel, the barrel just locks into the slide before each shot.
Personally i recommend the Crimson Trace lasser grips, as those can be adjusted for accuracy, and in my experience remain on target.