Barrel thread size?

[andym79]

Hi guys,

Firstly would anybody, know or be able to measure the thread size of a Greener GP shotgun?

Secondly how much steel does a gunsmith need to cut the barrel thread, for example if major thread diameter was 1.09", would a 1.12" shank be fine?

Thanks

[waksupi]

I've not messed with shotguns, so have no idea. You might try a dedicated shotgun forum with a gunsmithing section. Good luck!

[shunka]

Greetings Andy - if these guys over here britishmilitariaforums.yuku.com/topic/4314/Greener-Martini-Shotun-project are correct, they say it is GP, The Greener threads are 1.10"x14tpi.... Coyot yhs shunka

[Ballistics in Scotland]

Hi guys,

Firstly would anybody, know or be able to measure the thread size of a Greener GP shotgun?

Secondly how much steel does a gunsmith need to cut the barrel thread, for example if major thread diameter was 1.09", would a 1.12" shank be fine?

Thanks

The class act for this job is a thread micrometer. They can be expensive and rarely used, and the best are specific to a particular thread angle and fairly narrow range of sizes. Machinists threading on a lathe more often measure with an ordinary micrometer over three wires, two in the threads on one side and one on the other. The wire has to be of the right size to bear on the sloping flanks of the thread, not on the junction of flank and crest, as it is flank to flank contact you want. This gives only a comparative measurement, probably about 1.17in. for a 1.09in. OD thread. But if you are cutting a thread to match a good old barrel, that is all you need.

There is one helpful thing about the GP action. Most barrels have to be tightened up so that they are firmly located by pressure of the barrel shoulder against the front of the action. But the GP takedown system locates the barrel by clamping the receiver and barrel threads together. I would prefer a slightly larger barrel shank than 1.12in., but it would work. It possibly needs more accurate sizing of the barrel threads to the unclamped size of the receiver ones, and although American gunsmiths commonly used to thread Mauser barrels to 60degrees when the barrel is 55, I would prefer to get it right on this one. Root to crest rather than flank to flank contact is liable to loosen up.

Here is a barrel arranged for a similar action, though I don't know if it was ever a shotgun. A piece of ⅛in. or 3mm. square high speed steel has been silver soldered into a block, silver soldered in place. So you don't lose hardness in this tiny tongue which engages in the receiver slot to locate the barrel before clamping. Done this way you can choose whether the wooden forend bears on the receiver face at all, or perhaps with a sheet of brown rubber to even out pressure and exclude water.

[elk hunter]

Unless the Greener shotgun action is different than the normal Martini you need enough barrel diameter/metal to form a shoulder to butt against the front of the action to lock the barrel to the action.

[Ballistics in Scotland]

Like I say, I would prefer a bit more of a shoulder than a 1.12in. barrel blank would provide. But it isn't critical. The GP receiver is split at the bottom, and clamps onto the barrel threads by means of a transverse screw at the bottom front of the action. The little square stud in my picture fits in to a curved groove and comes up against the far side of the split, to make sure the barrel is turned to exactly the same position every time.

That screw (possibly ¼in. - 20 Whitworth, but check on it) can be replaced in the strongest steel if you feel the need, and fits in a much longer length of thread than any nut. So it shouldn't be weaker than the top of the receiver ring, and you can tighten up the threads really tight if you want to. I've known someone fire a few medium-range smokeless .45-70 rounds with the screw untightened, without mishap.