c-g-designs

ACTIONS 2,3 OR 4 LUGS ??.

        The question was recently asked on a Forum and, as usual, answers were multiple, ranging from the humoristics to the aesthetics !.

            I will try to reply under the technical aspect.

            First, some datas scarcely considered, however of essential importance :.

            A bolting system is defined by :

                        1°) Its number of lugs. Generalities.

                        2°) Lugs arrangement.

                        3°) Lugs geometry.

                        4°) Lugs total bearing area.

                        5°) Lugs total bearing angle.

            I think it is best evaluate each type, in commenting for each of them the hereover 5 points. We will remain on our subject of main interest, single shot long range Match actions, the repeaters generating other  constraints.

            A) 2-LUGS ACTIONS :

            1°) : It is the basic model. The bolt rotation  is 90°, although at least one model has been marketed  with a 70° reduced opening angle, but with lugs reduced in width and longer lugs, the option bringing nothing because reducing  points 4 and 5 ) hereunder . The lugs are protruding, ensuring  longitudinal guidance by means of rails machined in the receiver.

            2°) Conceived principally as repeaters, the lugs are placedvertically on closure, their bearing against the receiver counter-lugs being asymetric

            The exception to this rule is the SMLE system in which the lugs are horizontal on closing.

            3°) The lugs are of classic shape, with parallel sides and their outside form their external diameter. Their symetry is not always ideal, because of the presence of the on one side , and the ejector on the opposite.

            4°) Their bearingsurface is here minimal,  often inferior to 120°.

            5°) The total bearing angle is often inferior to 120°

            B) 3 LUGS ACTIONS :

            1°) It is the principle the best adapted to the ‘full diameter concept ‘ in which the lugs are of same diameter than the bolt body . The stroke guidance being here made by a separate mean, often the bolt stop.    

            This system is more and more used. Its 60° opening is easy and does not impair the prone shooter position when cycling.

            2°) The lugs can be of conventional shape, or of triangullar section with rounded apexes (Delta).  The Delta system will generalise, not only because of its superior characteristics, but also for its ease of realisation, as much on the bolt than in the receiver, necessitating no specific tooling (broaches and shape cutters).

            The angular disposition of the lugs is important, in order to ensure their  firm and even  bearing for all of them against the counter-lugs . The perfect disposition being 4,8 and 12 O’clock on closure, ensuring symetry on thevertical plane. This bearing,

            3°) The 3 lugs system offer the best ratio total bearing surface/total lugs bearing angle, equally repartited  in 3 surfaces at 120° that gives the ideal bearing.

            4°) The total bearing surface is usually 10 to 15% over the 2 lugs. This can vary depending on the lugs shape adopted.

            5°) The total bearing angle is far better  than those of the 2 lugs, close to the 160° for the classic, but close to the ideal 180° for the triangular Delta system. This is an important factor  for the intrinsic accuracy of the system.

            C 5°) 4 LUGS ACTION :

            This system, developped by Shultz-Larsen for their models 54 and 62 was used again by SWING and improved on the successive  models Paramount, C.G-RPA and C.G Millenium. Only those models were 4 lugs. 

            Its 50° opening (45 + 5 for the primary extraction and free the lugs) remain close of the 3lugs 60° is, although slightly heavier  in rotation, remain acceptable.

            The older models of tjhat type are now obsolete, progressively disappearing, but the more recent models remain actually  the most winners  of all the Long Range single shot Match actions.

            2°) The lugs arrangement at 45° (1h30, 4h30, 7h30 and 10h30)  of the vertical plane on closure is the most efficient as the lugs bears each against a solid surface of the receiver . For those of the right (R/H action) one lug bear OVER  and the second UNDER the shallow loading port.

            3°) The lugs are all of the same classic type . Since the Swing MK3, the lugs are guided by 4 rails in the receiver. But the Millenium has only 2 horizontal rails, the horizontal lugs being larger than the bolt body, while the vertical ones are same diameter as the bolt. This allow a smooter operation and improve feeding.

            4°) The lugs bearing surface is quite important  on this principle. But the lugs must be lapped to obtain equal bearing of the 4 lugs.

            5°) The total lugs bearing angle is is  close to those of the classic 3 lugs system at some 145°, but reduced only because the one more  lugs engagement chamfer.

            R.G.C