not an easy estimate, but it goes something like this
i have equal amounts of mags with fmj/tmj's and hp's that very between cartridges and capacities they hold. ar's are different in how many as it's different than pistols
in ar'sit's between 300 and 600 rounds total (regardless of how many in each mag) PER firearm of the same cartridge (example, 308win @ 10 ar's in that cartridge) could be 3,000-6,000 rounds (however the mags equal out to for average).
same per 5.56, 243win, 6.5gren, 6.5creed, 260rem, 6.5prc (undermined as of yet), 6.8spc, 277fury (not a finished build), 7-08rem, 7saum (not finished as of yet) 300bo and 308win.
then pcc's in ar's......9mm, 10mm & 45acp will be a different amount than pistols of the same cartridge.
no shotguns with mags yet....................yet.......................yet..........................