expendable ammo???

so i am not sure if ammo should be finite or infinite.

i like the idea of bringing resource managment aspect to ammo and make the players purchase and bring along enough ammo for a mission and OH NO we are running short things are getting tense this action packed sci fi pen and paper rpg sure is action packed

but in reality:  OH NO i forgot to subtract all the ammo ive been using the last few turns and did you subtract 5 shotgun shells last turn bert? no i did not.  boy this sure is a hassle writing numbers is boring

i tried a test run with expendable ammo and i feel that it just adds too much busy work to the combat.   and i want the combat to be as fast passed and exciting ad possible. 

making twice the number of trips to the pencil sharpener =/= exciting.