In my opinion pencil erasers, silicone, or leather would be too soft to provide the dampening necessary to do the job. I have seen hard nylon, as in A-Zoom, or spring loaded hard plastic. I suppose those are ok, but I would hesitate.

I have a de-cocker I made out of the butt of a shed deer antler with a piece of 1/2" round brass bar mounted. The solid brass certainly does the job. You would be surprised at the indentation the firing pins will make in the solid brass. It makes one realize how much force you are trying to dampen.

Here's a hasty pic of what I am talking about:

With the barrels off the gun, you firmly hold the brass against the face of the breach at the firing pin, and pull the trigger. Here's a look at how much of a dent the firing pins make:

After a period of use the tip gets distorted. I then just file it flat again and start over.

Again, I just don't think a soft material will provide any protection when decocking or dry firing. Of course, my decocker is no good for dry firing!

Best regards,
Curl