Adjustable firearm stock with passive tensioning mechanism
Embodiments of the disclosure relate to adjustable stocks for firearms and methods for installing an independently sprung tensioning mechanism. The adjustable stock comprises a stock body attached to a buffer tube, with a lever-operated tensioning mechanism. The mechanism includes a tensioning block with fins to grip the buffer tube, an indexing pin, and a retaining pin. When the lever is depressed, the tensioning block and indexing pin disengage, allowing longitudinal adjustment of the stock on the buffer tube. The tensioning block applies upward pressure on the tube, compensating for rotational tolerances during assembly. Both the tensioning block and indexing pin move independently when engaging with the buffer tube but move together when disengaging. The indexing pin is biased towards the buffer tube by a spring, while another spring biases the tensioning block. The lever engages the retaining pin to retract both the indexing pin and tensioning block.
1 . An adjustable stock assembly for a firearm, comprising:
a stock body configured to couple to a buffer tube of the firearm;
a tensioning mechanism within the stock body, comprising:
a tensioning body configured to couple to the stock body;
an indexing pin slidably arranged within an aperture in the tensioning body and having a first spring coupled within the indexing pin;
a first retaining pin coupled through a first set of apertures in the indexing pin and coupled through two additional apertures within the tensioning body, and wherein a first end of the first spring abuts to a bottom portion of the first retaining pin; and
a second retaining pin coupled through a second set of apertures in the indexing pin, wherein a second end of the first spring abuts to a top portion of the second retaining pin; and
a second spring coupled around the indexing pin between the tensioning body and the second retaining pin.
2 . The adjustable stock assembly of claim 1 , wherein the tensioning body has two fins extending from a top side of the tensioning body, thereby providing a u-shaped profile to the tensioning body.
3 . The adjustable stock assembly of claim 2 , wherein the two fins of the tensioning body are tapered.
4 . The adjustable stock assembly of claim 2 , wherein the two fins form a wedging friction fit engagement with a keyed extension of the buffer tube.
5 . The adjustable stock assembly of claim 1 , wherein the first retaining pin is actuated by a lever to retract the indexing pin from engagement with the buffer tube.
6 . The adjustable stock assembly of claim 1 , further comprising one or more stops within the buffer tube limiting movement of the indexing pin.
7 . The adjustable stock assembly of claim 1 , wherein the tensioning body and the indexing pin can move independently to accommodate tolerance differences between the stock body and the buffer tube.
8 . A method for installing an independently sprung tensioning mechanism in an adjustable stock assembly, comprising:
inserting an indexing pin through a first aperture in a tensioning body;
aligning a first pair of apertures in the indexing pin with a second pair of apertures in the tensioning body;
inserting a first retaining pin through the first and second pairs of apertures;
sliding a first spring into the indexing pin, wherein a first end of the first spring abuts against the first retaining pin;
inserting a second spring into a hollow in the tensioning body and around a portion of the indexing pin; and
compressing both springs to allow insertion of a second retaining pin through a second pair of apertures in the indexing pin.
9 . The method of claim 8 , further comprising coupling a first end of a lever between the first retaining pin and a keyed extension of a buffer tube by a friction fit.
10 . The method of claim 8 , further comprising coupling the tensioning body to a keyed extension of a buffer tube.
11 . The method of claim 8 , further comprising securing a cap to a bottom of an angled portion of a stock body to cover the independently sprung tensioning mechanism.