Thanks - that's another great idea. It just seems that depending on where I project my lines from the tips the balance shifts very slightly. Not a cause of concern, it's probably human error. I'm just being picky. I'll try the pipe and see if it gives me the same results as the tips and balance machine, give or take.

Just for reference - My 300S balances at 3" at the tips with a DA-50, pull-pull on the rudder, my ignition battery mounted on the engine box, and 2-2000Mah packs just over the landing gear, everything else is stock.