c-g-designs

FIRING PIN COIL SPRINGS.

A cpmpression coil spring is qualified by the values hereunder:

            -Outside diameter = ‘D’.

            -Wire diameter = ‘W’.

            -Free height = ‘L0’.

            -Length under maximal force =  ‘L1’.

            -Load at ‘L1’ = ‘P1’. This value represent the maximal force of the spring. If the spring is compressed over ‘L1’, ‘P1” does not increase. ‘P/f’ hereunder being to consider only between ‘L0’ and ‘L1’.

            -Rate = ‘P/f’. Increase of ‘P’ expressed in Newtpn per millimetre of compression between ‘L0 and ‘L1’. As the spring is ideally intended to be compressed at its maximal value, both at cocked andecocked positions,  the rate is secondary in our example case, except eventually if it affects the bolt lift effort if ‘P1’ is situated between the cocked and decocked positions..

            -Solid Height = ‘Sh”. Coming close to ‘Sh” in functioning is npt recommended. This is also a second reason why firing pin  springsare to be as lpng as possible , the ‘P1/’Sh being direct function of  of the ‘L0’ spring le ngth. Also, over-compression cause fatigue to the spring, affecting its specifications.

Elements to take into account  for a spring definition:

            1°) The more the diameter ‘D’ is reduced, the more the force ‘P1’ increase, the wire diameter ‘W’ remaining same. The diameter ‘D’ remain dependant of the firing pin rod diameter, on which the spring is to slip smoothly.

        2°) The more the free height ‘L0’ Increase, the mpre the rate ‘P/f’ diminish. It is again why a firing pin spring is to be as long as possible.

            3°) As said, compressed over ‘L1’, ‘P1’ does not increase anymore. As it is desirable to not ower-compress the spring, but same time maintaining a bolt lift  as smooth as possible, the spring length at bpth cocked and decocked positions will have to be slightly inferior to “L1’. At this condition , the spring will keep all its power duting  its stroke, thus contributingto obtain the maximum acceleration and force necessary to reach a faster lpcktime.

        4°) The condition 3°) above being realized, there will be no increase of ‘P1’ during the recocking (“P/f’ becoming non-operating. Therefore,, as there is no increase of “P’ between the decocked and recocked positions, the opening rotation will occur with no action of the spring rate (P/f x by the stroke in millimeters for up to 15,92N or rate x full or part of the FP stroke), and,without this extra spring compression, the bolt lift effort will thus be reduced to a minimum.

            5°) The force ‘P1’ is in reverse value to the FP stroke. For the 4mm (.157’) stroke of the C.G system , it will have to be 105-110 Newton (23-24 lbs/f). Reduced stroke and spring force contribute, together with the lightweight firing pin,to the locktime reduction.

In our example, the chosen spring will have the following characteristics (from the Associated Springs catalogue):

Reference C0360-059-3500.

            ‘D’       = 9,15mm. (.360’).                                                         

            ‘L0’     = 89mm (3 500’).

            ‘ W’      = 1,50mm. (.059’).                                                                                         

            ‘L1’     =  61,6mm (2.425’’).                                                                                    

            “P1’   = 108,2Newton (24,3lbs/f).                                                                                     

            ‘P/f ‘    = 3,98Newton/mm.                                                                                    

            Sh’      = 46,7mm (1.840’). 

            From the datas hereover, and particularily “L1’ the firing pin rod will have to be made for a spring length slightly shorter than the spring ‘L1’ at decocked position.

As “L1’ is 61,6mm (2.425’), the decocked length will then reasonably fixed at 60mm (2n.362’); therefore, the cocked height will be 56mm (2.205’). In those conditions:

            1°) The spring will always be shorter than ‘P1’. The recocking will then not to overcome a ‘P/f’ of 15,92Newton (3,98 x 4) (3,51lbs/f).

            2°) For the same reason, ‘P1’ will remain maximal all the FP stroke, therefore maintaining  energy and acceleration at maximal.

            3°) As in decocked position “P1’ remain to the maximal, this will prevent the eventual FP rebound  under  pressure rise and this will reduce the risk of craterisation to be virtually  non-existant.        

            The datas and observations above concern only  the C.G system. They are subjject to variation if applied to other models, depending on striker stroke, the spring characteristics and the weight of the mass in motion.

R.G.C.

12/2014.

Rev.01/2017

An other post will concern the C.G percussion system powered by spring washers (Bellevilles).