if your having trouble with range at XT, your gun has some serious issues. It's
grouping your talking about
lasers are useless, tactical lights are only good if you know how to use them, the silencer it just for looks unless it allows you to put a longer barrel in the gun, dual mag clamps are very useful, and slings are only really used if you have a pistol. Red dot sights are also a good investment for indoor games.
All i did to my UMP was add an RDS and improve its grouping, now its awesome indoors.