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Firing pin retraction surfaces

Pat C.

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78147
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Have this thread on the various M14 forums,thought I would add it here. Using demil receivers and my hand sketches to describe the function of the two cams and retraction face between them.
Sometime back I found the original tooling and manufacturing method basically consisted of a cam drum and later movement done with rack and pinion gear/handle . Using a double right angle milling head and stub endmill.

This was done by hand at a rate of 180 receivers per hour .one every 20 seconds.
Machined both cams and retraction face in one cut by lever.

The entry cam is not critical as long as the bolt can install easily ..Of course the rear face that connects the cams is ,as this stops the inertia at cyclic spear.
The cam in the firing pin slot wall is very critical as it pulls the FP out so bolt can unlock .
The two cams are helical one turn 2.45 LH ,and one turn 2.45 RH .The lead angle is 45 degree which is important and the forward edge of this cam is too.

You can see in the pictures the originals and I've shown a couple receivers I've done .
 

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Pat C.

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78147
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Posts
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Location
USA
Feedback: 2 / 0 / 0
Few more pictures to add , the cams are difficult to cut conventionally .Most cast receivers are casted done, don't know of a single manufacturer that produces the cam exactly.
The receivers I made ,It was a multi step process ,first finishing the bridge rear , radially shaving the area above trigger group slot, final radial shaving the retraction face.
The entry cam I broached with tiny tool steel blank, the retraction cam I milled with extended reach 1/8 endmill set on 45 degree lead angle and perpendicular to slot wall .
Blued the surfaces and opposing corners stoned to create the helix.
Worked perfect but very time consuming .
 

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