Seems to me that I have seen "No King but King Jesus" inscribed on something, though it may have been some contemporary piece. In Madison Grant's book The Kentucky Rifle Hunting Pouch there is a reference on page 130 of Charles Goodnight's rifle, which had engraved on the barrel "Seek ye first the kingdom of God, and his righteousness, and all these things will be added unto you" with a photo of the rifle on page 131, though it is a halfstock, rather than a longrifle. Great question, though, and it's generated a lot of interesting discussion.