Abstract:
This Regulated Bolt Carrier is a lightweight carrier having a built-in gas regulating gate. As a drop-in assembly it enables tuning of the gas system used in firearms of the AR-15 class. Adjustments of a continuously variable nature may be made quickly through the port door without requiring disassembly of the firearm. A gas “regulator gate” located under the gas key below a gas port inside the body of the bolt carrier itself is cut as a half-moon. Rotating the regulator gate on its axis changes the position of the half-moon cutout, blocking the entry of gas into the system. The regulator gate can be set anywhere from fully open to fully closed and is held in position by a small lock screw. For maintenance, the gas regulator gate can be pushed out of its bore via an access hole on the opposite side of the bolt carrier.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     This application claims benefit of U.S. Provisional Application No. 62/101,004 filed Jan. 8, 2015, entitled “Gas Piston Adjustment System for the AR-15/AR-10 Bolt Carrier”, which is incorporated here by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     The present application relates generally to firearms. More specifically, this application describes a mechanism operated by propellant charge energy to automatically open a bolt lock using an adjustable bleed of gas pressure from the barrel. 
     BACKGROUND OF THE INVENTION 
     One standard gas system used in AR-15 rifles is commonly referred to as Direct Impingement (DI). When a cartridge is fired, a portion of the expanding propellant gas is directed out of a gas port in the barrel through a gas tube and back into the upper receiver. As the gas then enters the bolt carrier through a gas key the bolt carrier is forced to the rear, unlocking the bolt. Thus, the cycling process begins, with the bolt ejecting the spent cartridge in preparation for acceptance of another shell. 
     Gases released through the bolt carrier serve to offset recoil and other impact forces in the firearm, subject to barrel length and bolt carrier weight. Additional variations due to ammunition will affect performance as a given amount of gas is directed back into the bolt carrier. Performance of the firearm in the ejection of spent shells may be tuned by controlling the amount of gas in the loop. A variety of solutions exist for regulating the amount of gas used in the system, most of which include an adjustable gas block on the barrel. 
     BRIEF SUMMARY OF THE INVENTION 
     When a gas-driven firearm is discharged, a portion of the munitions gases are directed from a hole in the barrel into a gas block directing the gas back into the bolt carrier. Performance of a particular firearm may be adjusted by controlling the amount of gas that is so directed. 
     The Regulated Bolt Carrier described here enables performance tuning of a continuously variable nature and allows it to be done quickly through the port door without requiring any disassembly of the firearm. A Gas Gate, located within the bolt carrier under the gas key, may be cut in a variety of shapes so that rotation on its axis either allows or blocks entry of gas into the system. After the gate is set by a user for a particular level of performance, it is held in the desired position by a simple locking device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Particular features and advantages will become apparent from the following description taken in conjunction with one or more of the accompanying  FIGS. 1-11  of the drawings: 
         FIG. 1  indicates a Regulated Bolt Carrier (RBC) ready for insertion to an AR-15 rifle; 
         FIG. 2  shows the Regulated Bolt Carrier (RBC) in position within an AR-15 rifle; 
         FIG. 3  is a perspective view of the RBC; 
         FIG. 4  is a detail to show location of critical elements within the RBC; 
         FIG. 5  is an exploded view of the RBC and related elements; 
         FIG. 6  is a top plan view of the RBC; 
         FIG. 7  shows a side view of the RBC; 
         FIGS. 8A-8C  depict gas flow paths within the RBC; 
         FIG. 9  is a cutaway view depicting gas flow past the Regulator Gate; 
         FIG. 10  depicts adjustment of the Regulator Gate; and 
         FIG. 11  depicts setting of the Lock Screw. 
     
    
    
     The following Reference Numbers may be used in conjunction with one or more of the accompanying  FIGS. 1-11  of the drawings:
       10  Rifle of AR-15 class     20  Upper Receiver     30  Gas Block     40  Gas Tube     50  Gas Port     60  Gas Key     80  Gas Path     100  Regulated Bolt Carrier (RBC)     120  Bolt     125  Gas Ring     130  Bolt Chamber     140  Regulator Gate, Adjustment Valve     150  Regulator Gate Lock Screw     170  Ejection Port Opening     180  Port Door, Ejection Port Cover     190  Exhaust Port   

     DETAILED DESCRIPTION OF THE INVENTION 
     Discharging a firearm causes the loaded projectile to be propelled through the barrel under influence of the pressure developed by the munitions gases. It is common in automatic and semiautomatic reloading firearms for a portion of the munitions gases to be tapped from a hole in the barrel and redirected through a gas block attached to the barrel. A gas tube then routes the gas back into the top of the bolt carrier. Such systems are commonly referred to as Direct Impingement (DI) systems since forces are transmitted directly to the bolt using the fluid pressure of the gas without any intervening mechanical pistons. 
     The release of expelled gases through the bolt carrier acts to mitigate forces of the bolt carrier in the system. These forces can be observed as recoil forces and as impact forces on the buffer tube and buffer tube springs in the firearm. Variations in ammunition may result in a range of gas pressures within a given system. Options for interchangeable bolt carriers, especially with the trend towards lighter weight bolt carriers, will affect performance as a given amount of gas is directed back into the bolt carrier. A firearm that allows for adjustment of the amount of gas permitted into the system can be tuned for preferred operating conditions with respect to observed forces, for spent shell ejection performance and reload cycle rate. 
     The presently described design facilitates the adjustment for optimal performance of a gas piston driven system such as that used in firearms based on the AR-15 and AR-10 platform as depicted in  FIG. 1 . A firearm  10  of this class will have a gas block  30  mounted to the barrel. Following discharge of the firearm a portion of the propellant gases from the discharged munitions is bled off of the barrel at the gas block  30  and routed through a gas tube  40  which extends rearward from the gas block. 
     A bolt carrier is inserted into the upper receiver  20  of the firearm. Insertion of a Regulated Bolt Carrier (RBC)  100  of the present design results in a configuration as shown in  FIG. 2  wherein opening of the Port Door  180 , also known as an Ejection Port Cover, exposes the regulation controls as being readily accessible through the Ejection Port Opening  170 . 
     When the RBC  100  is fully seated, a Gas Key  60  mounted to an upper surface of the RBC is coupled to the gas tube  40 . Gas from the gas tube enters the Gas Key  60  which routes the gas to the Gas Port  50  at the top of the RBC, as best seen in  FIG. 8A-8C . A Gas Path  80  provides fluidic communication through the Regulator Gate  140  into the Bolt Chamber  130  where the gas is trapped by a set of three Gas Rings  125  on the Bolt  120 . This drives the body of the RBC  100  backward relative to the munition that was chambered. The RBC continues to travel until it is far enough back relative to the Bolt  120  to expose the holes of the Exhaust Port  190 . The Exhaust Port will exhaust the gas that has been allowed into the RBC to relieve some of the gas pressure. 
     The maximum distance of travel between the Bolt  120  and the Regulated Bolt Carrier  100  is limited and once the limit is reached the entire assembly travels backward to eject the spent cartridge and load the next round. By controlling the action of the Regulated Bolt Carrier (RBC) the Regulator Gate  140  controls the impact of the RBC and consequently the amount of recoil in the system, as well as the reliable ejection of the spent shell. 
     As the Regulated Bolt Carrier travels backward the Gas Key  60  is decoupled ( FIG. 8B ) from the Gas Tube  40 . At this point the gas flow reverses direction within the Gas Path  80  as excess gas is vented back out of the Gas Key and through a cut in the face of the Upper Receiver  20  until the gas pressures dissipate. 
     As previously mentioned, venting also takes place through the Exhaust Port  190  behind the Port Door (Ejection Port Cover  180 ) after the Bolt  120  has completed the extent of its rotation and forward movement to eject and reload ( FIG. 8C ). Adjusting the Regulator Gate  140  to limit travel of the Bolt  120  to only what is necessary to operate reduces the amount of gas flowing into the Bolt Chamber  130 . This causes a reversal in the direction of gas flow and increases venting back through the Gas Key  60 . 
     At the heart of the Regulated Bolt Carrier (RBC)  100  is the Regulator Gate  140  with an optional companion Regulator Gate Lock Screw  150 , shown in  FIG. 3  with detail in  FIG. 4 , and additional views in  FIGS. 5, 6 and 7 . The RBC serves as a housing so as to position the integral regulating components to be accessible through the ejection port as was seen in  FIG. 2 . 
     Referring to  FIG. 9 , the Regulator Gate  140  serves as an adjustment valve to control the amount of gas that is directed into the Regulated Bolt Carrier  100  and the Bolt  120 . This rotary action valve provides for a continuously variable adjustment through an entire 360° of rotation to give a user complete control of the Gas Path  80  from fully opened to fully closed, that is, from no interruption to completely blocked. In the present context, the gas system may be adjusted from Unsuppressed to fully Suppressed. 
     The Regulator Gate  140  is, in general, a cylinder with a side cutout, shaped such as a flat or with a half-moon profile, acting as a ball valve. It is seated in a tightly toleranced bore to minimize leakage of high pressure gas around the gate, and can be pushed out of its bore for cleaning via an access hole on the opposite side of the Regulated Bolt Carrier  100 . 
     The Regulator Gate  140  is easily adjusted, effectively in real-time, by access through the Port Door  180  without disassembling the firearm in any manner. Opening the Port Door reveals the Regulator Gate  140  of the Regulated Bolt Carrier  100 , exposing it for adjustment as shown in  FIG. 10 . Adjustment is made by simply turning with a readily available wrench. 
     A lock screw, serving as a retention device, is threaded into the RBC parallel to the axis of the Regulator Gate  140  and offset from it such that a head of the lock screw overlaps an exposed portion of the Regulator Gate  140 . When the user has achieved a satisfactory adjustment of the Regulator Gate, the same wrench is moved to the Regulator Gate Lock Screw  150  which is tightened by turning clockwise ( FIG. 11 ) to hold the Regulator Gate in position. The Port Door is then closed before firing the next round. Readjustment of the Regulator Gate merely requires a user to reopen the Port Door, loosen the Regulator Gate Lock Screw by turning counterclockwise, make the desired adjustment, retighten the Lock Screw, and close the Port Door. 
     Given the ease of adjustment of the present design, one might easily overlook the fact that, among configurations that are adjustable, essentially all other designs require the bolt carrier to be removed from the upper receiver in order to make any adjustment. Using the present design, adjustment is easily accomplished with the bolt carrier in its position for operation. 
     Often gas adjustment is accomplished on the gas block which is typically attached at about mid-length of the barrel. Locating the adjustment on the bolt carrier not only makes the adjustment more accessible, but also moves the adjustment further away from immediate contact with the barrel. This helps to reduce particulate buildup, alleviates concerns about corrosion, and reduces the need for cleaning. 
     In addition to its location the orientation of the Regulator Gate within the Regulated Bolt Carrier (RBC) offers advantages beyond ease of adjustment. Since the body of the Regulated Gate is oriented with its axis perpendicular to the flow of gas, it will not “back out” due to vibration of repeated firings. This overcomes a problem which occurs with designs that utilize a gate that is threaded into the gas flow path wherein a tip of the threaded gate obstructs the gas flow, an example of which is U.S. Patent Application Publication 2015/0241149 to McMillen for “Adjustable Gas Key for Autoloading Firearm”. 
     In 2015 GEMTECH (Boise, Id.) introduced a Suppressed Bolt Carrier for use with some direct gas impingement rifles. It purports to allow a shooter to select either a suppressed or an unsuppressed setting, with no intermediate adjustment being provided, without any permanent modifications to the firearm. However, selection of one or the other setting requires an inconvenient removal of the bolt carrier from the upper receiver. 
     Beyond location and orientation, the presently described inline, pass-through gate allows passage of debris even when partially restricted. The shape of the gate itself tends to minimize turbulence as gas flows smoothly past the gate. This reduces dead space where residue may accumulate. 
     The components and methods described here can be adapted to any firearm based on a gas piston driven system, not just those based upon the AR-15 or AR-10 platforms. Since the described regulator system can only regulate the amount of exhaust gas delivered to it, insufficient exhaust gas in the system may limit adjustments to a less than favorable condition. If the gas supplied by a given system is found to be insufficient for desirable regulation, adjustments may be made upstream by resizing the orifice of the barrel-mounted gas block, or the load may be adjusted in the ammunition. 
     The intent of the methods described here is to provide a firearm user with a convenient means to adjust the force of recoil of a bolt carrier at the bolt carrier. The method also provides for easily repeating the adjustment to achieve a proper ejection pattern of expired shells from the firearm. 
     It will be recognized by those skilled in these and related arts that many variations of the described embodiments are possible. The regulator gate may be reconfigured to operate in a linear rather than rotary manner. Such alternatives include a sliding gate or orifice plate where gas flow is controlled by inserting or retracting a slide into a channel in the bolt carrier. Such a gate may present a solid face against the gas flow, or it may have a shaped or tapered cut out. Positioning of a gate may be aided by adding detents to provide tactile feedback during adjustment.