doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com top screw out of time

If the wood has dried or shrunken for some reason, the top screw will rotate too far and be to the right of the index point. It can be caused by having the stock off and retightened to hard, thereby compressing the wood. I have fitted shims to correct this if the amount is slight. Often though, it can't be very thick or it will index at a point above the surface of the tang. It is generally caused by a wood problem and not the screw or head seat wearing. If it won't turn far enough to index, it is often due to interference in the screw head seat, under the top tang or interference in the action inletting.

Ok. Can you explain where this shim is placed to correct the pin timing?

Just under the pin. But this is so obvious that I think you are trying to make some other point.

Nothing nefarious here, dude. I’m asking because I’ve never seen this or heard of someone adding a shim to correct pin timing. It’s a serious question. Relax.
Every gunmaker I know just makes a new pin that tightens & times correctly. Back in the day some gunsmiths used to recommend having the head welded up and then refit. I and many others thinks it’s faster and easier just to make and fit a new pin.

So…..I’m curious and would like to see how this method of shimming to time pins works and how it’s done.

Shimming is just a at home patch. Not a gunsmith fix.

A proper shim repair includes gluing a thin layer of wood in place and re-inletting, I have done it a few times and it works fine in certain situations.

As to the OP and his screw head that is out of time, follow Bushveld's advice, figure out the why and then what the proper repair would be.

The way I've seen it done is by making a tiny flat washer out of the thinnest shim stock you have, then placing it under the head of the pin and tightening it down, then verifying the position of the slot. If more is needed you go to the next thicker shim stock. Simple trial and error.

Sorta like shimming the hook on a double gun that's not worth paying to have it put back on face. Like my BSS duck gun.

Dustin, I've read about adjusting the timing of a screw slot by doing exactly what Stan is saying, as an alternative to either machining a new screw or making adjustments to an existing screw by either adding or removing metal from the bottom of the screw head. The "shim" or washer can be made out of very thin sheet metal, plastic shim stock, or even waxed or oiled paper.

If you know the pitch of the screw threads, you can even calculate how thick the shim needs to be to move the slot the desired amount. In this case, the head needs to turn 90 degrees either way to align the slot at a 6:00-- 12:00 position. So if the thread pitch is 32 TPI, you would divide 1 by 32 which would equal .03125" for each full turn. Then divide that .03125 by 4 and the result would be .0078125" for a quarter turn. So a shim or washer .008" thick would get you very close to the 90 degrees of movement needed to align the slot.

Of course, there are various ways to get to the same result which have been mentioned. One other way would be to cut the countersink for the screw head a wee bit deeper. But it may just be a matter of a screw which is either turned in a quarter turn too tight or too loose. If it is already good and tight with a good hollow ground screwdriver, cranking even tighter with a brace or using more force also risks exceeding the yield strength of the screw, or even breaking it

That is interesting, Steven. Of all the gunsmithing books I've read I don't believe I have ever read of that technique. I would like to learn more detail about how the thin layer of wood is created and glued in.

Thanks for bringing up that procedure. If there is anyplace you know of that I can read more concerning it, I'd surely like to know about it.

When I competed with a M-21 Winchester this was a common problem as the trigger pulls were maintained by the position of the trigger plate distance in relation to the receiver. This was controlled by the thickness of the stock in the grip area. The stock bolt would need to be adjusted to compensate for humidity and about every other thing you can imagine. It was that critical.
I fixed this by building a metal tube inserted into the stock for the bolt to go through and milled it to length so I could snug up the bolt and problem was solved. This was done on two M-21 guns and was a permanent fix.