EVERYTHING he owned which was not jointly titled with someone else (with right of survivorship), like real estate or bank accounts owned in that way, is part of his estate; a decedent's estate is made up of everything he or she possessed which did not pass to others outside of probate, such as via joint title or through a previously set up irrevocable trust. Therefore, the gun is part of the estate; any oral discussions that you would get it are irrelevant, since only a properly executed (or signed) and witnessed written will controls what happens to property after someone dies. Of course, if ou are his only child (stepchildren don't count for this purpose, unless specifically left something in a will), if he does  not have a currently surviving spouse, it will go to you anyway, albeit after probate.