Greener Martini GP takedown

[andym79]

Hi guys just wondering are Greener Martini GP takedowns suitable for using as an action for centrefire rifles?

The brain is just thinking would be a handy way of interchanging barrels!

But does that split design have enough strength for the pressure?186529

Also if it is suitable how big is that barrel shank, anyone know the thread size?

What level of modification would be needed to make it function with a rifle cartridge?

[Ballistics in Scotland]

I think it does. I know of someone firing medium-range .45-70 rounds when he had forgotten to tighten up on the locking screw, with no ill effects. Id consider a good fit on those threads to be more important than with most rifles. I wouldn't, for example, cut 60 degree threads to fit the 55 degree receiver threads, which plenty of American gunsmiths find satisfactory with Mausers. But basically it is a good system, probably stronger than interrupted threads. If you imagine the top of the receiver threads to be a sort of hinge, the locking screw is about three times as far from it as the sides of the threads. That is leverage, so it is clamping the threads much harder than the force of the locking screw.

For most centrefire rifles you ought to bush the firing-pin to a smaller diameter. Oh, and don't forget to tighten the locking screw. Otherwise it should be find for the purpose.

[andym79]

That is good to hear!

So the sort of pressure are we talking about, would be stuff like 32-40, 38-55, 40-65 or 45-70 at lowish pressures?

You would have some serious meat around a 32-40 chamber! At a guess, would the thread size be close to 1" as a12g is .729".

I guess you would definitely need a new extractor made as a 1g one would be something like .880"?

So a different bolt would not be needed for a different rim size as the greener breech block is flat and the rim of the cartridge sits in a recess in the barrel not in a recess in the bolt as in lever actions rifle?

So the main thing would be to bush the firing pin and an extractor would need to be made for each rim size?

[Ballistics in Scotland]

That is good to hear!

So the sort of pressure are we talking about, would be stuff like 32-40, 38-55, 40-65 or 45-70 at lowish pressures?

You would have some serious meat around a 32-40 chamber! At a guess, would the thread size be close to 1" as a12g is .729".

I guess you would definitely need a new extractor made as a 1g one would be something like .880"?

Could you try to get a bolt and extractor from .303 martini, I wonder if they are sold separately?

Those are the sort of cartridges which have often been used in rifles like this, and should be safe if it is unimpaired and the job is done properly.

The military Martini thread, which was also used in the Lee-Enfields, is 1in. - 14, but conversions aren't suitable for a shotgun cartridge larger than 20ga. I don't know whether the problem with going larger is thickness of metal in the threads, or difficulty of insertion. So the GP threads are considerably larger and the breechblock is wider. I doubt if the change to a .303 extractor is possible, and am sure it isn't easy. They are in demand, and very hard to find without a rifle attached. I would silver solder a bar across the top (one continuous piece at first), and file it to suit the cartridge head. It probably needs to be hardened and tempered to stop the limbs twisting, and I would use needle-thickness pins to hold it in place while the solder is loosened by heat.

Here is an extractor emerging from a piece of steel, in this case D2 air-hardening to simplify the heat treatment. It is a big job, even with my small milling machine. The secret of forceful ejection is that it first contacts the extreme rear end of the extractor for powerful leverage, then as soon as the case is moving, it contacts the curve near the pivot for less force but more speed.

186532