No.4 trigger stoning..and other question

[Bruce_in_Oz]

Captain Laidler has provided some information on this subject in the past.

Here is my five lira worth:

On the cocking piece, the ANGLE and FLATNESS of the front face are CRITICAL. If the angle is too steep, the sear will slide straight off, thus causing a VERY dangerous condition. If too shallow, the trigger operation will be safe, but ridiculously heavy. Before you start playing, test the performance of the striker spring; if it is too soft, playing with other parts is pointless.

Furthermore, of you get carried away with "stoning", you may do another nasty thing:

Cause mis-alignment of the cocking piece and safety "locking bolt".

If the cocking piece sits too far forward at full cock, the slots in the side will not line up correctly with the driving-flat on the end of the locking bolt. That's the correct name for what most folk call the "safety catch". If this happens you will either chew up the locking bolt or, if really bad, you will not be able to engage it at all.

Not sure about No4s, but on a SMLE, the dimensional allowance from axis to bent of the top arm of the sear is 1.6018" Max, 1.5988" Min, a tolerance of 0.003".

On the cocking piece, the angle of the full bent (front face) is 86 deg, 10 min. It is a dead FLAT surface.

I do not have the materials data for No4 cocking pieces, but SMLEs were a carefully heat treated CARBON steel. In fact, the heat treating was quite complex, there being three "zones"; full-bent, middle with safety stud, and the rear "button" area. Final dimensions and finish were done AFTER the correct hardnesses were achieved; LOTS of precision grinding.

Correctly assembled, the system should meet the following criteria:

1. The locking bolt (little flat on the end of the lever shaft) should freely engage the full-cock and half-cock notches on the lower left side of the cocking piece. The lever should be drawn back with the fore (trigger) finger, (thus, conveniently, keeping it off the trigger). Correct drill: "ON with the finger OFF with the thumb". If there is heavy drag, there is probably a dimensional problem with the cocking piece, sear or both. NOTE: when the "safety" is engaged, the cocking piece sits clear (to the rear) of the sear, When you rotate the locking bolt forward (off/FIRE), the cocking piece is returned to rest on the tail of the sear.

2. In the "fully-cocked" position, the trigger should have two stages. These are determined by the two "bumps" on the trigger itself. On "first' pressure, the sear should be moved SLIGHTLY down the face of the full bent of the cocking piece. This SHOULD also (all angles and dimensions being correct) move the cocking piece to the rear VERY slightly.

Now, here is the IMPORTANT bit. If you relax this first pressure, the sear spring SHOULD force the sear back UP to its resting position and the cocking piece SHOULD move forward to its previous resting position. If this return movement of the sear does NOT occur, you have a potentially dangerous situation. It also indicates that the sear spring could be weak or that one or more of the angles, dimensions, hardness and surface grade (smoothness) of the components are NOT to spec.

A lot of "range" rifles seem to have been subjected to "redesign" of the trigger function and thus have "single stage" triggers or ludicrously light set-ups. If you are firing single shots at a slow pace, you MIGHT get away with this: forget about fire and movement / "run-downs", especially if the safety assembly has also been "customised".

Check out the "Knowledge Library" for further technical data and procedures.