Unmarked aside from a matching numbered receiver, bolt and a few small circular proofs, this is a Spanish contract pattern Mauser rifle equipped as a pressure test gun. The rear sight has been deleted, and mounted just ahead of the chamber is the test assembly with a gas piston and a screw-adjustable anvil protected by a steel cover. In operation, a brass test disc (not included) is inserted between the piston and anvil, and the depth of impact made by the piston tells the engineers how much pressure was generated by the test cartridge. Smooth straight wrist stock with "21" stamped on the comb.