Side folding stock assembly with concealed hinge arrangement

1. A hinge arrangement for a firearm assembly comprising:

a first hinge portion adapted to be mounted in one of a firearm assembly and a stock assembly;

a second hinge portion adapted to be mounted in the other of the firearm assembly and the stock assembly; and

a translation linkage position between the first and second hinge portions for permitting the first and second hinge portions to move into and out of spaced apart alignment with each other, the translation linkage being located substantially within the first and second hinge portions when the first and second hinge portions are moved toward each other, wherein one of the hinge portions is provided with a ramp surface structure and the other one of the hinge portions is provided with a locking notch structure to engage the ramp surface structure and lock the hinge arrangements to each other.

2. The hinge arrangement of claim 1 , wherein each of the hinge portions is provided with external mounting structure adapted to be received and retained in the firearm assembly and the stock assembly.

3. The hinge arrangement of claim 1 , wherein each of the hinge portions has a sidewall formed with slot structure.

4. The hinge arrangement of claim 1 , wherein each of the hinge portions includes an interior mounting space for mounting the translation linkage.

5. The hinge arrangement of claim 1 , wherein the hinge portions have internal mounting bases which are coplanar with each other when the hinge portions are moved into spaced apart alignment with one another.

6. The hinge arrangement of claim 1 , wherein the translation linkage includes a set of swing arms swingably mounted on hinge pins, and configured in a stacked overlapping relationship.

7. The hinge arrangement of claim 6 , wherein the hinge pins include a first set of hinge pins fixed relative to the hinge portions, and a second set of hinge pins movable relative to the hinge portions.

8. A folding firearm stock assembly comprising:

a shoulder stock assembly having a hinge arrangement including a first hinge portion adapted to be mounted to a rear portion of a firearm assembly, and a second hinge portion mounted to the shoulder stock assembly; and

a translation linkage located between the first and second hinge portions for permitting the first and second hinge portions to move into and out of spaced apart alignment with one another, the translation linkage being located substantially within the first and second hinge portions when the first and second hinge portions are moved toward each other, wherein one of the hinge portions is provided with a ramp surface structure and the other one of the hinge portions is provided with a locking notch structure to engage the ramp surface structure and lock the hinge arrangements to each other.

9. The firearm stock assembly of claim 8 , wherein the second hinge portion is mounted substantially entirely within the shoulder stock assembly.

10. The firearm stock assembly of claim 8 , wherein the shoulder stock assembly includes a buffer tube for receiving and retaining the second hinge portion therein.

11. The firearm stock assembly of claim 10 , wherein the buffer tube includes a locking collar which is engageable and disengagable with locking structure on the first hinge portion.

12. The firearm stock assembly of claim 11 , wherein the locking collar is mounted for sliding and rotatable movement on the buffer tube.

13. The firearm stock assembly of claim 11 , wherein the locking collar includes a tooth structure which is engageable and disengagable with a ramp surface structure on the first hinge portion.

14. The firearm stock assembly of claim 8 , wherein the translation linkage includes a set of swing arms swingably mounted in a stacked overlapping relationship on a set of hinge pins fixedly and movably mounted in the hinge portions.

15. A firearm assembly comprising:

a shoulder stock assembly having a hinge arrangement including a first hinge portion mounted within a rear portion of a firearm assembly, and a second hinge portion mounted within the shoulder stock assembly, the shoulder stock assembly and the rear of the firearm assembly being movable into and out of locking alignment with one another; and

a translation linkage located between the first and second hinge portions for permitting the first and second hinge portions to move into and out of spaced apart alignment with one another, the hinge portions and the translation linkage being substantially concealed from view when the shoulder stock assembly and the rear portion of the firearm assembly are moved into locking alignment with one another, wherein one of the hinge portions is provided with a ramp surface structure and the other one of the hinge portions is provided with a locking notch structure to engage the ramp surface structure and lock the hinge arrangements to each other.

16. The firearm assembly of claim 15 , wherein the hinge portions are mounted so as to prevent any axial and rotational movement within the rear portion of the firearm assembly and the shoulder stock assembly.

17. The firearm assembly of claim 15 , wherein the shoulder stock assembly includes a locking collar rotatably and slidably mounted thereon, the locking collar being engageable and disengagable with locking structure on the first hinge portion.

18. The firearm assembly of claim 15 , wherein the translation linkage is located substantially entirely within the hinge portions when the hinge portions are moved into spaced apart alignment with one another.