Rail interface systems and methods of mounting accessories to a firearm

1. A rail interface system installed on a firearm equipped with a first firearm accessory mounted to the firearm with at least one mounting assembly on top of a receiver of the firearm, the mounting assembly having a first rail interface facing in an upward direction on top of the receiver and a clamping assembly that includes first threaded fasteners adapted for releasably clamping the mounting assembly to the first rail interface, the rail interface system comprising:

a second rail interface configured to couple with a second firearm accessory;

clamping nuts each having a threaded bore by which each of the clamping nuts is threaded onto a corresponding one of the first threaded fasteners; and

second threaded fasteners threaded into threaded holes of the clamping nuts to secure the second rail interface to the mounting assembly of the first firearm accessory, wherein the first and second threaded fasteners and the threaded bores and the threaded holes of the clamping nuts are coaxially aligned and secure the second rail interface to the mounting assembly;

wherein the second rail interface is positioned laterally to one side of the receiver at an elevation lower than the first firearm accessory mounted to the firearm with the mounting assembly.

2. The rail interface system of claim 1 , wherein the second rail interface comprises a pair of parallel longitudinal rails and slots that extend laterally between the pair of parallel longitudinal rails and are spaced longitudinally along the length of the second rail interface.

3. The rail interface system of claim 1 , wherein the second rail interface is a Picatinny-type rail interface (MIL-STD M1913), a Weaver-type rail interface, or a NATO STANAG 2324 rail interface.

4. The rail interface system of claim 1 , wherein the second threaded fasteners comprise screws that pass through holes in the second rail interface and are threadably coupled to the threaded holes of the clamping nuts.

5. The rail interface system of claim 4 , wherein:

the threaded bores are in shanks of the clamping nuts; and

the threaded holes are in heads of the clamping nuts.

6. The rail interface system of claim 5 , wherein each of the heads of the clamping nuts has a hexagonal form so that a wrench can be used to tighten the replacement clamping nut onto the mounting assembly.

7. The rail interface system of claim 1 , wherein the second rail interface faces in a lateral direction that is perpendicular to the upward direction of the first rail interface.

8. The rail interface system of claim 7 , wherein the elevation of the second rail interface relative to the firearm is higher than the receiver.

9. The rail interface system of claim 1 , wherein the first firearm accessory is a telescopic sight.

10. The rail interface system of claim 1 , wherein the firearm is a rifle.

11. A method of using a rail interface system to adapt a firearm equipped with a first firearm accessory mounted thereto to mount a second firearm accessory, the first firearm accessory being mounted to the firearm with at least one mounting assembly on top of a receiver of the firearm, the mounting assembly having a first rail interface facing in an upward direction on top of the receiver and a clamping assembly that includes first threaded fasteners releasably clamping the mounting assembly to the first rail interface, the method comprising:

removing installed clamping nuts from the first threaded fasteners;

securing a second rail interface to the firearm by threading replacement clamping nuts onto the first threaded fasteners to releasably reclamp the mounting assembly to the first rail interface, and then threading second threaded fasteners into threaded bores of the clamping nuts, the first and second threaded fasteners and the threaded bores of the clamping nuts being coaxially aligned and securing the second rail interface to the mounting assembly; and

coupling the second firearm accessory to the second rail interface.

12. The method of claim 11 , wherein the second rail interface faces in a lateral direction that is perpendicular to the upward direction of the first rail interface.

13. The method of claim 11 , wherein the second rail interface is mounted to the mounting assembly with the first and second threaded fasteners and the threaded bores of the clamping nuts such that the second rail interface is positioned laterally to one side of the receiver and the mounting assembly at an elevation relative to the firearm that is higher than the receiver but lower than the first firearm accessory.

14. The method of claim 11 , wherein the first firearm accessory is a telescopic sight.

15. The method of claim 11 , wherein the firearm is a rifle.