Electronic .........i managed to get a pair of custom fitted AXIL SportEar plug made a few years ago at the Melbourne SHOT Expo
They are excellent - and i would say their are many other similar electronic custom fitted and semi-custom plugs out there. They amplify background noise and eliminate loud noises such as recoil blast.
However i dont use these at the range - they come into their own when i am out stalking but for the range i use electronic muffs in the form of SportEar M2's from memory.
Work very well also.
C