I never considered the store using it, I just thought the OP was speculating on the end customer's use of it, as a guard for a bank or in a prison.

I expect rural drug stores in 1930 did not employ guards, but I suspect they may have sold guns.

An intermediate option is that a pharmacist may have ordered it and kept it in the cash drawer or some other hiding place. Even in rural Ohio drug stores probably feared robbers - whether for cash or drugs.