Harris Engineering Number 3 Adapter Remington Semi-Auto. OpticsPlanet Inc is an Authorized US Distributor for Harris Engineering Bipods. For Remington semi-automatic rifles Models 4 74 and 7400. Package Contents: Harris Engineering Number Adapter Remington Semi-Auto 3 We offer the complete line of Harris Engineering Bipods. For our complete selection of products by Harris Engineering on sale please visit our Harris Engineering page. For more Bipod Accesories please visit our Bipod Accesories store section. Harris Engineering Number 3 Adapter Remington Semi-Auto