Well...that would have to be my FP-45 Liberator pistol. Or...at least it was the most unusual I have owned--as in past tense, sadly. I wont go into that in this post. But for sure of all the guns I have owned, this was the most unusual or rare...at least for me anyway. Maybe a close second would be a .36 cal Kentucky squirrel rifle that was passed down from a couple generations ago...still in the family but I gifted it to another family member years ago. LOVE those old BP long guns!!