This is a Harris Engineering Rotating known as the Bipod, model S25.
Harris Engineering's Ultra-Light 12"-25" Rotating Bipod is manufactured with heat treated steel and hard alloys. It clamps to the Q.D. stud of most bolt action rifles that have a conventional stock design. Carrying your rifle with a sling or shooting off-hand is not impeded by the use of a Harris Bipod. Folding legs have completely adjustable spring-return extensions (Except for Model BRM and LM).
Features:
Attaches to a Sling Swivel Stud
Legs Extend from 12 to 25
Three Piece Standard Legs
Swivel Base tilts to compensate for uneven terrain