[Ron Wood]

This is just my WAG but I would guess it is a 1920's or so era Swiss rework by a commercial firm/gunsmith. The chamber marking to me does not look engraved, but rather an "aftermarket" die stamp, definitely not an official Swiss Waffenfabrik roll die. I have no documentation or source to substantiate this, just an observation based on the quality of workmanship and overall appearance of the piece. As Lugerdoc has pointed out, this barrel configuration is sometimes encountered and I think he is correct that it is an expedient modification to repair an otherwise serviceable barrel that has suffered front sight/muzzle damage. Again this is just my opinion, so take it with a 5 pound bag of salt.