Abstract:
The invention presented here is an add-in part designed for the M4 and similar commercial AR-15 rifle variants or any other weapon using an adjustable multi position receiver extension based on the M4 pattern. Its purpose is to be installed in the longitudinal adjustment slot of the receiver extension tube limiting the buttstock&#39;s maximum extension travel to a preselected position.

Description:
REFERENCE TO RELATED APPLICATIONS 
     This application claims an invention which was disclosed in Provisional Application No. 61/395,947 filed May 20, 2010, entitled “Buttstock pre-adjustment block.” The benefit under 35 USC §119(e) of the United States provisional application is hereby claimed, and the aforementioned application is hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This application relates to the field of firearms particularly telescoping buttstock mechanisms. More specifically it concerns an improvement to the M4 style and its derivative telescoping buttstocks found on many modern adjustable-for-length firearms. 
     2. Description of Prior Art 
     The telescoping buttstock has been fielded by many nations since the advent of modern mechanized warfare moved soldiers into vehicles. Telescoping is defined as an axial longitudinal movement collinear with the barrel and action assembly of the firearm. Early submachine guns utilized a wire type telescoping buttstock in order to decrease the overall length of the weapon when it was not in use. The advantage to such a mechanism is the speed with which the arm can be readied from its collapsed position. Many styles of telescoping buttstock have been created since their introduction but none have been as ubiquitous as the M4 style that was originally created for the M16 family of rifles. Roy in U.S. Pat. No. 3,348,328 took the basic use of a telescoping buttstock and added the extra feature of a number of stopping positions located vertically in the buffer tube or receiver extension. Each position may be locked into by depressing the lever to disengage the locking pin in one position and sliding the stock lengthwise to another position and releasing the lever. This then allows the locking pin to engage vertically in the desired locking detent position. This shall henceforth be referred to as the M4 type adjustable buttstock. 
     Thus the trigger pull length could be tailored to each shooter that is issued a rifle. This new family of telescoping (or adjustable) buttstocks is today available for and used on rifles, submachine guns, shotguns (as shown by Kay in U.S. Pat. No. 6,662,485) and even belt fed machineguns. It has become the de facto standard due to its end user adaptability. It has a flaw in use, however, in that with the exception of the furthest position a user is unable to immediately ready their weapon from the completely collapsed position. This is due to the fact that there are a number of possibly positions and the user must pass over the undesired detents in order to find that which they prefer. This can be time consuming and in a combat situation, life threatening. 
     Fitzpatrick et al in U.S. Pat. No. 7,762,018 B1 creates a new assembly of parts to accomplish the length of pull adjustments but also includes the ability to preset the buttstock to a desired position. This however requires an entirely new buttstock to be installed on the gun after previously removing the older, more commonplace and standardized version. 
     SUMMARY OF THE INVENTION 
     The present invention allows for any firearm with an attached M4 pattern collapsible buttstock to be able to preset to the users desired length. This includes civilian designated AR-15 and AR-10 variants as well as any other firearm that uses a receiver extension shaped tube on which to mount a buttstock using a longitudinal groove and multiple locking detent positions. The buttstock pre-adjustment block consists of a portion that locks into a locking detent position in the receiver extension and a portion that interferes with the rearward axial movement of the attached collapsible buttstock. The invention allows the firearm operator to preset the desired length by installing a buttstock pre-adjustment block into the receiver extension (buffer tube). By doing so, the user can immediately pull the stock to its desired length without needing to count spaces backwards or forwards. This is particularly useful for any shooter who may be wearing armor or heavy clothing and would need a position located in the middle of the receiver extension. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  shows the preferred embodiment of the buttstock pre-adjustment block. 
         FIG. 2  shows possible alternate embodiments of the buttstock pre-adjustment block. 
         FIG. 3  shows the method of installation. 
         FIG. 4  shows a partial cutaway of an installed buttstock pre-adjustment block in a complete buttstock assembly. 
         FIG. 5  shows the buttstock extending to the limit set by the pre-adjustment block. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An M4 (AR-15, AR-10, etc.) style telescoping buttstock as shown in  FIGS. 4 , and  5  has a stock portion  24  as well as a release lever  26  and a locking pin  28 . This allows the user of the weapon to actuate the release lever  26  until locking pin  28  retracts from one of the numerous locking detents  20  located in receiver extension  18 . The buttstock  24  then is allowed to telescope axially while the locking pin  28  slides lengthwise in the receiver extension&#39;s longitudinal groove  22  until the desired position is located. This mechanism allows-for-a multitude of length of pull settings for a single given firearm as well as a more compact overall length for use in transportation scenarios. 
     The buttstock assembly is often in its most collapsed state when the firearm is not being used; that is actively carried or fired. This could mean that the firearm is simply sitting in a storage rack or has been collapsed for entry and exit of vehicles, buildings, or any other confined area. The transition for a firearm with a collapsible stock in a storage or transportation position to one of readiness can take fractions of a second or much longer, depending on which position the user desires. 
     For example, if the user&#39;s preferred position is where the buttstock is fully extended, the amount of time is minimized as the motion to retract the collapsible buttstock portion  24  until the locking pin  28  collides and stops against the rearmost position of the longitudinal adjustment groove  22  and releasing the adjustment lever  26  allowing the locking pin  28  to drop into the rearmost locking detent  20  can be done in one muscle movement. If however the user&#39;s desired position is not the rearmost, the movement becomes much more complicated. Should the user desire any middle position, they then must count locking detent positions  20  back or forth until the most comfortable or necessary point is found. This can take several seconds and in the heat of battle can be difficult. 
     As shown in  FIG. 4 , the Buttstock pre-adjustment block  10 , when installed into a receiver extension (buffer tube)  18  limits the total travel that a buttstock  24  can travel. More specifically when the pre-adjustment block&#39;s upper cylindrical section is inserted into the receiver extension locking detent  20  as shown in  FIG. 3  with its lower rectangular portion filling the longitudinal groove  22  in receiver extension  18  it effectively removes the detent position in which it is located as well as any positions behind it by blocking the locking pin  28 . 
     Thus with a buttstock pre-adjustment block  10  installed before the buttstock assembly  24 , as shown in  FIG. 3 , onto the firearm receiver  16  the most desired position can be selected as the maximum length available. This means that the shooter can immediately adjust the buttstock from its storage position to its readily usable position in a single movement using the least amount of time possible. 
     The buttstock pre-adjustment block&#39;s installation can be done without training or tools. Installation is as follows as demonstrated by  FIG. 3 .
         (1) Remove the current buttstock (not shown) assembly. This is usually accomplished by fully extending the locking pin  28  and sliding the buttstock  24  rearward off the back of the firearm&#39;s receiver extension tube  18 .   (2) Place block&#39;s  10  cylindrical protrusion into the detent position one space behind the preferred locking position (i.e. if you want it set to position five, place the block in position six.) Doing this will prevent the locking pin inside the buttstock assembly from travelling past the desired locking position.   (3) Reinstall buttstock assembly while holding locking pin at full extension until it has passed over the block. The buttstock assembly keeps the pre-adjustment block from falling out.       

     Accordingly, it is to be understood that the embodiments of the invention herein described are merely illustrative of the application of the principles of the invention. Reference herein to details of the illustrated embodiments is not intended to limit the scope of the claims, which themselves recite those features regarded as essential to the invention.