Howdy
As the others have said, there is no need to do this. Lower the hammer manually before putting the gun away. There is no need to store it with a snap cap in it.
The only time I store a gun with a snap cap in it is with a gun with an internal hammer. The hammer on my Winchester Model 12 is internal. There is no way to lower the hammer manually. I don't like to leave the hammer cocked for a long time, so when I put the gun away I put a snap cap in the chamber, then pull the trigger to drop the hammer. The snap cap in the chamber protects the firing pin.
P.S. There is no need to spray anything on the snap cap when doing this, I never do. Been doing it for a long time now.