As long as its semi accurage (within 5* to 10*) then don't worry about it. Not all engines like to run at the same temp. I'd just start to worry if the temp gun starts reading over 270*F There really isn't a reason to run an engine that hot, it will wear out very quickly.

Temp guns are good when you start off because its a visual indication of what is TOO hot. But as you learn how to listen to a nitro engine you won't need a temp gun as much. I still use a temp gun when I question what i'm hearing from my nitro engine.