It's a tact switch. It's only rated at 1A/32V but I've never had one fail on me unless I got juice in it.
KSJ0M21180SHLFT C&K Components | Tactile Switches KSJ0M21180SHLFT | Onlinecomponents.com
Surprised it didn't fail. If you read the manufactures datasheet, the max current is 50ma.
Put a volt meter across the switch when firing it and see what the voltage drop is.