I have no need of snap caps, have also seen a gun discharged when it's owner believed he was relieving the mainsprings with snap caps...but used live rounds.

I do store my guns uncocked, but "snap" the guns w/ barrels off with a plastic screw driver handle or a wooden dowel. Reassemble the guns, and I'm done. Why someone would want to store a gun with anything in the chambers is beyond me, but each to his/her own.