This is exactly what I do Rich, with the model and calibre marked on the card, though I like to use a different colour fob for each brand of gun.
It makes it all so much easier at the Bash when rummaging in the hatchback for a particular rifle amongst maybe 8 similar looking cases!
Atb, Clogger
Job for a rainy day if you have a few.
I have taken the wrong rifle to the range more than once.
Better than taking the rifle and forgetting ammo box