Only makes sense , to have at least one box of ammo available for each gun to be sold . My LGS specializes in the old & unusual , if he gets in a gun in odd caliber he doesn't usually stock , he will seek some out . ( If it's still made , something like .32 rimfire , not so much .)
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In times of ammo panics , availability flip flops . Popular common calibers sell out first . You will then see shelves only having things like .41 , 10mm , .357 Sig , etc .
But once the supply chain starts trickling in , the mfgs will concentrate on a handfull of popular cals , and won't start making the slower moving cals until they catch up on demand for the bog sellers .