The sales have stopped because everyone who needs/wants gun has enough guns in their arsenal. If I have enough guns to protect myself, why would I need extra expenses? The marginal utility of a gun purchase is almost non-existent once we have enough guns!
What you cannot enough have is the ammo!
How hard is it to go into an ammo biz? One would think new ones would be popping up with the new demand unless the overhead was forbiddingly daunting.