That would scare the heck out of me.  An emotionally unstable drinking alcoholic firing guns off casually?  A recipe for a terrible accident, or worse.  Plus he's firing them off with no warning outside your house?  Plus I imagine the alcohol, and/or his own stinkin' thinkin', makes him think he's totally in control and nothing bad could ever happen.  (Unless, even worse, he wants something bad to happen.)

For me, saying he couldn't bring guns over would be like asking my AH not to drive drunk.  He'd say, "I'd never do anything dangerous, no way, I'm totally on top of things here."  But he doesn't have the stability or the good judgment to keep from doing it.

If I were in your shoes, I'd set the boundary that he shouldn't be at my place.  In my experience of alcoholics, that's the only way the ensure that they won't do whatever it is at my place.  If I asked mine not to drink, he'd say "No worries, I won't drink a drop," and then he'd drink anyway.  If I asked him not to drive drunk, he'd say "I'd never do that," and then he'd do it anyway.  He didn't have a gun, but if he did and I asked him not to bring it, he'd say "I won't do that" and he'd do it anyway.  He might do it just because he thought he knew better than me, but he might also do it because when someone tells him not to do X, he immediately shows he "can't be controlled" by going and doing X.  So in my experience, the only way to stop him from doing this or that at my house would be to draw a boundary that he couldn't come to my house.  That boundary might be hard to enforce at first, but it's easier to enforce than trying to wrestle a gun out of his hands.

Take good care of yourself.  It gives me the heebie-jeebies that he brought a gun over to your house and showed it to your son and fired it -- and what does he think he needs a silencer for?  I think your sense that he was demonstrating his power (kind of a threat) could be right on.  Do you know the book The Gift of Fear?  It talks about how our fears can be sensible warnings.  I hope you won't allow his crazymaking behavior to put you at risk.

Silencers are illegal without the right permits...He went through all the paperwork and official background stuff in order to get one...and he has no criminal record. 

I'm still just always walking on eggshells with him...I'm afraid of him and I'm always wondering what will set him off....

Thanks for the support, I need all the help I can get....