No4 Trigger problems - Help appreciated.

[jss]

I have a couple of No4 Mk1's with trigger problems and I am confused as usual.
One, a Savage Mk1* sometimes sticks at half cock on (possibly timorous) second stage trigger pull. A straight edge on the bottom of the cocking piece shows a significant 20 or 30 thou gap at the sear interface end whereas my more pristine rifles have cocking pieces with little or no gap.
The other, a POF No4 Mk1 has a replacement bolt(My MkII bolt works fine in it but that has a good cocking piece) and if first stage pull is released before firing, the bolt travels upwards resulting in a single stage trigger at the next pull.
I realise that these are typical No4 problems but I am not sure how or whether to fix them.
1)With a straight edge along the bottom of the cocking piece; Should there be any gaps?.
2)What is the reference point for the height of the sear with respect to the body(action) and what is the angle of the sear from that refence point?.
3)These problems could be fixed in several ways, but which is correct and/or acceptable and in which order;
a)New bolt or cocking piece or possibly sear.
b)Grind of the back of the sear to let it sit up slightly and grind a bit off the lower lug with a bit of grinding of the trigger bumps.
c)Check the trigger guard is sitting flat. Should the trigger operation be checked with a standard length collar without the wood fitted, or should adjustments be made after woodwork is fitted and collar adjusted. (I'm Having a problem with that too).
d) Do sear lengths/heights differ much?.
e)Do the Bumps on the trigger differ and/or sometimes need adjusting?.
g)Is it OK to have a single stage trigger pull by removing the first bump on the trigger?.

Finally, is there anyone out there with a stock of No4 bolt bodies, sears, cocking pieces etc at a reasonable price so that I don't have to spend months on auction sites?.

Information

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[Bruce_in_Oz]

Please do not grind ANYTHING!

First, check the "Knowledge Library" for Peter Laidler's contributions on the subject.

My 2 cent's worth:

When you squeeze the trigger, it may end up "half-cocked". This is actually a safety feature.

Make sure that the bolt and cocking piece BOTH have the little "elliptical" safety stud in place. These two little "bumps do a little dance around each other as the bolt is cycled. They are there to prevent the striker getting close to the primer, except when the bolt is locked down fully.

I have seen several ex-"fullbore" target rifles that have had the stud on the bolt bodt "removed". I have no idea what the purpose of this supposed to be.

If this feature is missing from your bolt, get a new bolt. If the one on the cocking piece has vanished, get a new cocking piece.

If your bolt is floating about such that, upon release of first pressure, the sear does not return to its rest position, several things may be the cause:

1. Either the body or bolt are terminally flogged out,

2. The angle in the full bent (front face of the cocking piece) may have been "adjusted WAY out of spec, angle / smoothness - wise.

3. The cocking piece is REALLY loose on the striker thread and is floating up and down with the sear stuck on the front.

4. The sear spring is REALLY tired and is not returning the sear to its proper "rest" position.

If the receiver is worn, you are out of luck. If the bolt body is the problem, see all the lessons in acquiring and fitting a new one; it is a straighforward job but requires skill and patience.

Final notes: the "grip" bit of the cocking piece should NEVER be able to contact the rear of the bolt body whilst the bolt head is correctly fitted. Striker protrusion is set by the Collar of the striker resting on the rear of the bolt head. If some bozo has "adjusted" the rear of the bolt head to increase striker protrusion, they will have stuffed up all the relationships of the cocking piece to the safety mechanism.

If the striker is screwed too far into the cocking piece, the cocking piece may strike the rear of the bolt body before the striker has reached the back of the bolt head, resulting in poor striker protrusion and misalignment of the safety notches wuth the locking bolt.

If the striker sits too far farward in the cocking piece, and in the unlikely event you can apply the safety with the action"de-cocked", the striker may well be still resting ON the PRIMER, which is NOT a good thing.

See the "Knowledge Library" for more details.

[jss]

Thanks for taking the time to offer advice Bruce. Everything looked OK on each rifle and the POF is now OK having fiddled with the new woodwork to get muzzle pressure and a flat seating for the trigger guard. Either the sear was fouling or the trigger guard angle was causing inadequate second stage contact. I am surprised it took so long for the Mk2 trigger change to come into use given this apparent design flaw!.
I am waiting for a new cocking piece for the Savage although the one on it looks good. I will scour the knowledge base for further clues on the half cock trigger fault.