c-g-designs

VI)-ACTION DESIGN.

CONCEPTION OF SINGLE SHOT  MATCH ACTIONS

5-BOLT

The Bolt represent  a real challenge. It is in itself a piece of functionnal engineering art

Functions a Bolt and its components have to perform:

---A): On opening:

-Primary extraction,..

-Extracting the empty case.

-Re-cocking the firing mechanism.

-Ejection of the fired case (if ejector fitted as this is often optional, many shooters preferring to recove their empties by hand).

---B): On closing:

-Feeding the round.

-Transferring  the firing system from Bolt Sear resting notch of the bolt cocking ramp to trigger Sear.

-Ensure bolting.

All those functions are closely interlinked and require extremely precise machinings, diameters, lengths, shapes and angular timing.

Bolt must be wear and stress resistant . Choices of treatments and finishes are of the upmost importance. It is not recommendable to use surface-hardening steel but full core-hardened (quenched) one instead…

Surface finishes must be determined for wear resistance and low friction coefficients.

A competition Bolt must also, like the Receiver, be STIFF. Lightening the bolt is risking to make of it the weak element of the assembly. Fluting, mostly helicoidal, is to be avoided as much as possible and only when ultimate weight saving is  needed.

-Lugs:

The possible lugs arrangements are:

--- 2 lugs, Bolt opening angle 70° to 90°.

--- 3 lugs, Bolt opening angle 60°.

--- 4 lugs, Bolt opening angle 50° (not 45° as one can think at first).

The 3 lugs design is now prevailing as it offer many advantages:

--Best total bearing angles over all models,

approaching the 175° on well designed systems. This concept of total lugs bearing angle is important although often neglected. Every effort must be made to obtain the maximal angular bearing total of the lugs.

--Large bearing and shear areas.

--Best compromise in Bolt lift angle and ease of Bolt

lift.

--The triangular shape (Delta with truncated diameters) is the simplest  geometry  ensuring simple machining and the largest Lugs shear and bearing areas of all the principles. Extractor and Ejector does not impair with lugs on such a system in front locking design, but are situated in non-critical locations instead .

The Lugs can be either:

--A)- Of a diameter larger than the Bolt body to serve as linear guidance of the Bolt.

    Positives:

-Good Bolt linear guidance.

    Negatives:

          -Need specific machining (broaching or EDM machining in Receiver and complex shaping of the Bolt Lugs).

-Bolt is not supported by its full circumference and this severely affect centering.

--B)-

The Lugs and Bolt body are of same diameter:

This principle allow the Bolt to be centered in the Receiver on practically its full circumference and this all the way long.

The Bolt is guided in its linear motion by a slot milled along the Bolt body and is prevented in rotation by a Key, generally constituted by the Bolt Stop itself.

Receiver counter-Lugs are not broached, but milled or sink EDM cut. This also is more concentric and accurate than broaching..

The full diameter bolt concept is ideally suited for the 3 lugs arrangement.

Just to mention:

-The multiple lugs design allowing in principle a reduction of lugs diameter and increased bearing surface. But this makes even bearing of all the lugs quite problematic. Also, lugs shear area is reduced.                                                                                              

-The interrupted threads Lugs system, a variant of the above, which is used only confidentially, as prone to create headspacing problems.

Both arrangements are mostly used in 3 Lugs full diameter Bolts.

R.G.C