The listing acts as if this is a Finnish modification for a recoiless Mosin Nagant. I've never seen such a thing
Here is the description from the seller:
FINNISH , MODEL: MOSIN NAGANT SUB CALIBER DEVICE , CALIBER: 7.62 X 54 , BORE IS FAIR, WORN, LIGHT PITTING. MOST PARTS MARKED WITH NUMBER 5 EXCEPT BOLT, FITS FINNISH LAHTI L39 ANTI TANK GUN. ROUND BARREL NO SIGHTS, HEX RECEIVER, STRAIGHT BOLT HANDLE, HAS STEEL VENTILATED SPRING ASSISSTED ACTION INSTALLED ON BARREL, MISSING TRIGGER PIN, INCORRECT TRIGGER LACKING HOLE. METAL FINISH SHOWS SCRATCHES, HANDLING MARKS AND WEAR. CONSIGNOR NOTE: FINNISH MARKED (SA) LAHTI 7.62 X 54MM SUB CALIBER UNIT FOR A LAHTI L39 ANTI TANK RIFLE. RECOILING MOSIN NAGANT ACTION IN A SLIDING TUBE WITH AN AIR DASH POT TO EASE RECOIL AND FACILITATE RETURN. NO MOUNTING BASE AND INCORRECT TRIGGER ( NO HOLE FOR CABLE) SEE MARKO PALOKANGAS'S MONUMENTAL BOOK ON FINN FOREARMS FOR INFO ON THE UNIT. IT IS FINNISH SA MARKED UNDER THE RECOIL COLLAR. A RARE AND NEVER SEEN ITEM IN NORTH AMERICA.
Here is the description from the seller:
FINNISH , MODEL: MOSIN NAGANT SUB CALIBER DEVICE , CALIBER: 7.62 X 54 , BORE IS FAIR, WORN, LIGHT PITTING. MOST PARTS MARKED WITH NUMBER 5 EXCEPT BOLT, FITS FINNISH LAHTI L39 ANTI TANK GUN. ROUND BARREL NO SIGHTS, HEX RECEIVER, STRAIGHT BOLT HANDLE, HAS STEEL VENTILATED SPRING ASSISSTED ACTION INSTALLED ON BARREL, MISSING TRIGGER PIN, INCORRECT TRIGGER LACKING HOLE. METAL FINISH SHOWS SCRATCHES, HANDLING MARKS AND WEAR. CONSIGNOR NOTE: FINNISH MARKED (SA) LAHTI 7.62 X 54MM SUB CALIBER UNIT FOR A LAHTI L39 ANTI TANK RIFLE. RECOILING MOSIN NAGANT ACTION IN A SLIDING TUBE WITH AN AIR DASH POT TO EASE RECOIL AND FACILITATE RETURN. NO MOUNTING BASE AND INCORRECT TRIGGER ( NO HOLE FOR CABLE) SEE MARKO PALOKANGAS'S MONUMENTAL BOOK ON FINN FOREARMS FOR INFO ON THE UNIT. IT IS FINNISH SA MARKED UNDER THE RECOIL COLLAR. A RARE AND NEVER SEEN ITEM IN NORTH AMERICA.