REAR LOCKING SYSTEM

Why I do like the concept.

 A): Angle of pressure (forces transmission):         

            -In a Front Locking  system, the angle formed by the two (or multiple) Lugs bearing surfaces from the centre of the bottom of the case head recess is a very wide angle. On a commercial action of reference, it is:

                        -98° at the root of  the Lugs.     

                        -112° at the outside diameter of the Lugs.

            Possible slight variations from one model to an other can exist, but is neglectible.         

           It can immediately be noticed that the forces spread at those angles creates a ‘flexion’ effect as the force is exerted at centre, and the hold on the outside as per the above angles.

            -In a Rear Locking system, this angle is very shallow. On the INCH, it is:

                                    -12° at the root of the Lugs.

                                    -14° at the outside diameter of the Lugs.     

            It can immediately be noticed that this closed angle is creating a buttress effect, transmitting the forces in almost a straight line with the bore axis. No flexion, only compression forces that the generous cross sections of the Bolt (and Receiver) compensates in harmony with no buckling possibility.

B): Bolt travel:

            The transfer of the lugs to the rear allow an important reduction in Bolt travel:

            - On Front Locking systems lenghtwise allowance must be made for the Bolt Lugs and Receiver Counter-lugs, that the Bolt head has to override to reach closure position. The cartridge to be chambered has to accomplish the same increased movement.

            -On the Rear Locking system, the Lugs are situated behind the Loading Port, and the cartridge can be fed directly.

            By comparison;

            -On the same Front Locking Action of reference hereover mentioned, the Bolt travel is 107mm, (4.210’), when it is only 85mm (3.346’) on the INCH,  the later allowing also longer cartridges cases.

            This also have a big influence in Cheekpieces profiles and heights possibilities, as this reduced Bolt travel impairs much less the cheekpiece position.

C): Bolt Face and feeding:

           -The absence of necessary cuts to ensure the Lugs shape allow to have a perfectly cylindrical Bolt Head, surrounding entirely the cartridge head. This has also allowed the use of a wider extractor.       

            -Cone breach was the obvious solution, not easily achieved in front locking designs. The feeding of a round, moreover thanks to the absence of Lugs raceways, is the smoothest possible.

D): Lugs arrangement:

            -The Rear Locking of the INCH allowed a specific Lugs disposition, as, when closed, each Bolt Lug is situated geometrically, with one lug at top (12 O-clock when closed), and the two lowers symetrically in the horizontal plane (4.30 and 7.30 O-clock respectively),. This mean that each Lug is situated behind a consequent section of the Receiver, and also backed by a circular strong section of the Body behind them..

            This is to compare with the Front Locking, where one of the lugs is always immediately ahead of the Loading Port, or, in the case of a two Lugs design, bearing vertically in the axis of two uneven side sections, the R/H one (RH action) being considerably reduced by the Loading Port crosss-section.

E): Barrel Shank:

            -The INCH reduced Bolt travel allow a significant increase of barrel shank lenght  (35mm-1.378’), however keeping the action the shortest of its category (187mm –7.368’ OAL).

            Two closely toleranced cylindrical registers, one behind the threaded middle part, the other at front  center the barrel, the middle threaded section acting only as what a thread  is intended for: screwing and tightening.

            This arrangement makes the barrel change extremely easy, and with absolutely no zero shift.

            Also, the inside collar allow a double bearing of the barrel shoulders: against the Receiver front face, AND against the inside collar. Shoulders bearing surface is at least 30% more than a conventional fitting.

            On the subject of easy barrel interchange, the generous dimensions of the Delta Lugs arrangement allow an excellent holding area for the short Action wrench.

F): Concentricity:

            As, contrarily to the front-locking actions  systems, in which the presence of a counter-lugs neck between barrel shank recess and Bolt raceway compels the borings to be machined in two operations, one for the front and the second from the rear, with subsequent concentricity problems, the INCH bores being stepped down from front to rear, the borings are realised in a single machining operation, thus ensuring an absolute  concentricity.

G) Lugs recess maintenance;

            The location of lugs recess far away from the chamber protect it from combustion abrasive deposits. Direct accessibility and geometry allow easy maintenance.

R.G.C

06/2009