Not from the back side of a revolver, but you could tell by looking at the front of the cylinder if it was an unshrouded type.TexasTornado wrote: I've never seen or handled a blank, but would it look any different loaded into the weapon?
I can understand the additional drama/realism of using blanks, but I think we've shown here that it's an unneeded risk. Add the sound effects via some speakers if needed.
In any case, the idea, the correct way is you make the gun different in both visual and physical ways. I have modified real weapons for blank use. the chambers were plugged in a way that did not allow real loaded ammo to chamber, but blanks would.
In the semi auto I did, this also allowed for reliable cycling with a modified slide and recoil spring.
I've seen folks just do a barrel plug
and not address the issue of real ammo being capable of being loaded 
