doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Hinge Pin-Removable or Rotate

I had originally posted this under the Fabrique Nationale post but not sure many might have followed it.

When I went and picked this gun up I noticed a slight movement which I thought was in the for-end, but noticed it was in the barrels. Gt it home and it was .003 of face with a feeler gage.
I happened to notice that there was screw slot where the hinge pin was. After driving out the center pin, removed screw covers and found that the hinge pin had a slot in it also. I could move it but not unscrew it. Found in the front bottom of the receiver, a small screw, removed it and I was able to take the hinge pin out.
I made a measured drawing and put it back until where it originally was. Rotated it one quarter turn . Put barrels back on and is not off face now. Spot punched pin and removed and drilled for set/retaining screw, put covers back on and should last-----. Pin looks to be made of tool steel by the way the chips were when drilling.
Question is, is this a common thing on European guns, and do any American guns have this feature?
Were the Europeans smart enough to know that these things do wear and so did this feature. I'm sure there are a lot of steps to do this, but this particular gun, Cockerill Special, was probably their lowest graded gun.

The other question is, in measuring the pin that went through the hinge pin and covers, it measured .139 or 3.53mm, hinge pin measured .334 on unworn area which is 8.48mm. The hinge pin threads where .315 or 8mm x 1.25 and the threads were 9. All but the threads aren't common metric sizes. They are usually in even increments. It would be hard even on a 1 to 1 lathe to constantly get those measurements without filing.




I didn't notice until these pictures of the piece of wood chipped off the for-end that follows the receiver line. Pretty neat.

That's pretty smart stuff, good thinking. And kudos to you for discovering it.

I believe the hinge pin could be rotated to compensate for wear on the Model 21. Winchester also made various sizes of hinge pins, so if there was too much wear, you could simply replace with the next size larger.

Good show! It sort of proves what I read recently, that pins are made of softer steel than the hooks. I imagine especially on pins made easy to remove.

The only problem with rotating the hinge pin is that it does not compensate for hook wear or out-of-roundness. You will get some/most return to face, but not like new (it is very unlikely that the hook has no wear or out-of-round). A new, oversize hinge pin is a better approach. If you have M8-1 1/4 threads on the pin, it should be a possibility on metric lathes.

Cockerill was the steel supplier, not a gun making firm.

Good work. Nice to see applied mechanics in action.

Hi JDW, you did everything right but you can also do it even righter if you want. I'm presuming that you backed the pin out a quarter turn and not tightened it a quarter turn??? which of course would have been better. Ideally the pin should be tight with cap supported and both parts actually in the frame supported also. Otherwise the pounding it gets on firing results in looseness sooner rather than later. That's why it takes a lot of fitting to make a perfect cross pin. An amount of work generally not justified except where the gun has special value. Only you can decide. I'm also presuming you have access to a lathe and know how to cut threads up to a shoulder??? I've found O1 steel fine for the purpose, perhaps not the nicest machining steel in the world, but it will take a polish to a fare thee well and doesn't need to be ( in fact shouldn't be ) heat treated.

Rotating the pin one quarter turn was the easy way, the set/retaining screw in the front of the receiver holds it in place from moving. It is not bottomed out on the shoulder now. I still had to file the head slightly because the cocking rods pivot on the pin that is driven through the hinge pin and caps.

If there was wear on the barrel hook the gun would still be off face because the hinge pin is/was to a uniform size of .334 diameter.


In cutting threads to a shoulder, an under-cut is usually made at the shoulder so that it can bottom out.

Yes of course I understand perfectly, I would have done the same. Well maybe taken a couple of thousands off the back side of the cap and sunk it in a quarter turn instead. Yes undercutting threads at the shoulder is the normal way to do it but when I really care I take the thread right up to the shoulder. Put tool behind work and cut away from shoulder or do it very, very carefully the standard way.

If you have enough height adjustment in your tool holder you can also turn the tool upside down, run the lathe in reverse & feed away from the shoulder. Just a little easier to see than on the back side, but same thing really.

Yeah Miller, I've done that too. It's nice to know that there are real machinists who read these posts.