Oh, man.
I SOOOO feel for you. The gun thing would have been the last straw for me, too.
I suggest you have all your locks changed immediately.
You have done the right thing, believe me. You aren't a failure. All kinds of good people wind up being addicts or have addiction in their families. Once the drugs take over, only the addict himself can do anything about it.
I STRONGLY urge you and your wife to seek out Nar-Anon, for families and friends of addicts. There's also a terrific forum here for you under "family and friends".
Picking your son back up and giving him "another chance" at this point would accomplish absolutely nothing, except give him the opportunity to continue to victimize you. When and if he manifests a sincere desire for help, you can revisit the idea of a treatment center, but you cannot let an active addict take over your home--especially when you have other kids in the house.
Hugs, dad--you are doing the right thing.