I am making a few snap-caps in calibers not offered by manufacturers I'm aware of, and am undecided WHAT to put in/fill the primer pocket with. I've been thinking of simply filling with Thermogrip hot-melt glue -- or, G.E. Silicon. "Googling" this I came across ideas ranging from using automobile tire rubber cut to fit; similar with pencil erasers; and even balsa wood!
I'm seeking experienced advice: what works best? The firearms I'm making these snap caps for are quite old, and mostly take rimless (.30 Rem, .32 Rem, .35 Rem) cases. I bought a Model 8 Remington a while back with a broken firing pin, and gunsmith -- perhaps as old as the firearm -- suggested in his opinion, the quickest way to break a center-fire firing pin is to dry fire it -- sans a cushion (e.g., snap cap) for it.
Thank you, and BEST!
georgerkahn