Simplest would probably be to use two commands, E.G.
fire
Press ? key and hold for 0,01 seconds and release
Pause 0,05 seconds
with the "Repeating" option set to "Repeat continuously until stopped"
cease fire
Kill command, 'fire'
Release ? key
If you're looking to trigger the command using another keyboard key, you can use a single command with a loop instead, E.G.
Start Loop While : Keyboard Key 'F12' Is Pressed
End Loop
Start Loop While : Keyboard Key 'F12' Is Not Pressed
Press ? key and hold for 0,01 seconds and release
Pause 0,05 seconds
End Loop
The first loop makes sure the trigger key is released before starting the second loop, so the latter doesn't stop immediately.