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No worries, Rhodes;

Here is some information for you. From my time spent in Australia, I know that you fellows like the technical side of how thing works, as do Americans. Australians sort it out in your "sheds" and we Americans work it out in our "shops"

On high quality hand fitted and proper made double rifles the "little" barrel extension seems to work quite as well as the Greener style cross bolt, because it is one of the combined pair of mechanisms that cause the barrels to be locked to the face of the standing breech; and secondly to pull the lumps of the double rifle away from the hinge pin during firing. It is a system that is not generally known how it works to the casual observer, and it takes great skill and experience in fitting during the building of the rifle by the likes of Purdey, Hollands, and Boss.

On a DR built by the three named above the "draw" of the action contacts and rubs against the circle of the DR rifle barrel lumps during the final closing and just before the locking slide or bolt fully locks the barrels in place to the action. Further rubbing movement during the closing (via the arc created from the hinge pin)of the barrels causes the rub to become a firm contact between the circle and draw, thereby pulling the barrels to the rear when the locking slide and the third fastener (Purdey 2nd style patent or Hollands similar design)move fully into their respective locking positions.

The little third fastener being situated behind the breech face and rearward of the barrel breech end, creates a great deal of additional strength due to he mechanical advantage of the third fastener being further from the hinge pin center point than the locking portion of the standard locking slide that moves into the two slots of the barrel lumps(also a Purdey design "the Purdey locking bolt".

Several high quality (translated as high dollar cost usually of new rifle in excess of $100,000.00 each)even go to the trouble of redesigning the circle for replaceable circle "shoe" that can be replaced and fitted after years of service and much firing of the rifle has caused the circle and draw contact not to force the barrels to the rear enough to move the front lump away from the hinge pin during closing and locking of the barrels to the action. There is also two schools of thought of how the the draw and circle should be formed on double rifles; with one school favoring the traditional circle shape or form and the other favoring the form to be in a straight line angle where more surface area can be had for final locking of the circle and draw together.

I favor the straight the angle and this is how I am going to finish the action of a double rifle that I am now in the midst of.

Years ago the Italians(Senior Zanotti introduced it in 1906) changed the design of the standard Purdey double lump and extended the rear lump back further than the English gunmakers and rifle makers do. This is why when you examine a Italian double rifle or double gun (or even a Spanish double rifle with maybe a third fastener) you will notice that a milled slot has been cut into the lower face of the breech to allow the longer rear lump to extend behind the standing breech. I like the Italian lump design, but some one of my English gunmaker does not and explains his reasoning of which I cannot remember at this time. As mentioned above the Spanish have adopted the Italian long lump on their shotguns even with third fastners.

The Greener cross bolt is probably the best of them all, but you find a great deal of variance in how gun and rifle makers believe the cross bolt should be fitted and where it should be tapered. I have never been able to find in writing by Greener how he intended the cross bolt to be fitted. I favor fitting it with the pin firmly contacting the rear of the barrel hole up to just above the hole's center line; and further for the pin to fit firmly against the bottom of the barrel hole. To my mind, a DR using the Greener cross bolt should have added length in the action standing breech to compensate for any possible strength loss of drilling a 7mm or so hole across the standing breech face. The barrel extension should also be made of steel of proper wearing ability.

Of course, building DR's with very wide lumps and large diameter hinge pins along with super strong high yield strength steel, can relegate third fastners to the past I suppose. However systems that move the barrels to the rear away from the hinge pin seem "just correct thing to do" in my simple mind.

All the best;

Transvaal