This probably has a REALLY simple answer!
How do i put an object into an invisible layer?
I need to put my bullet into an invisible layer for my game.
How do i do it?
Thanx
CrAzY Dan 8)
Select the Objekt in Objektmode,press M,select one of the 20 Layers…klick OK. Your Objekt has moved in to the Hidden layer now 
How do i select a different layer? 
to select a layer just press the numbers 1-9 and 0 to get to layers 1-10 and alt 1-9 and 0 to get to layers 11-20, if you push shift you can select more than one layer
you can also press (next to one) to show all layers and shift to undo that
also you can animate what layer it’s on, just go to the frame you want it to change layer, press i, and insert a layer key
Select the Objekt in Objektmode,press M…it should a Button appear(Screenshot!)select one of the 20 Layers…klick OK. Your Objekt has moved in to the Hidden layer now
greets ________Blendworker