Bloodnative,
I want to apologize to you and the other readers for allowing myself to be drawn into this "mudslinging". I would like to explain my credentials and then I shall bow out of this forum permanently. I am a relatively new member here, having joined about 2 months ago. I am 62 years old with 3 grown kids and 3 grandkids. I point that out to show that I'm not some pseudo-expert, teen-age troll.
I own a 9" x 54" South Bend Lathe with milling attachment and thousands of dollars worth of tooling. I'm no tool and die maker but I have become fairly proficient in the use of this equipment over the years. I have been welding, both gas and electric, for 35 years. My educational background is heavy on chemistry and physics. My father spent 5 years with the Royal Canadian Electrical and Mechanical Engineers during the war, teaching welding at a trade school in London. He spent 30 years as a welding engineer with Massey Ferguson. He spent several years on loan to a company in Chicago helping to develop high-temperature metal-deposition systems for re-entry vehicles in the US space program. He then spent 15 years as an inspector and tester with the Canadian Welding Bureau. You could say that I have had the best advice that money can buy when it comes to the topic at hand.

I have hunted and owned guns for 50 years. I have been in love with double guns and double rifles for 30 years. Like you, I would never be able to afford a double rifle, short of winning the lottery, so I decided to build one. I was well aware of the potential dangers and spent literally 100's of hours on research, correspondence, etc. I have built 3 so far. The first was a 12 gauge rifle, as I was only working with pressures up to about 12,000 psi, for my first attempt. I have killed 7 whitetails with that gun and it has fired hundreds of rounds of Lightfield slugs. The second was a .22 Hornet which again has fired thousands of rounds and puts 5 lefts and 5 rights into 2 inches at 50 yards with iron sights. The third was a 10 gauge by .54 caliber Cape Gun which is my deer gun during our muzzleloading season. I am currently building a .450 #2 NE which I plan to take back to Africa to shoot a second Cape Buffalo.

I see discussions like this one quite often, where some guy is right where I was 20 years ago, anxious to build a double rifle and thirsting for the knowhow and advice. I thought that I might have some useful information to offer here, based on experience, and some tough mistakes. I thought that I had presented that information in a polite and well-thought-out manner. Mr. Moon obviously thought otherwise, as a re-read of his post after mine will show. He basically told me and the rest of the world that I don't know what the hell I'm talking about, and he did so in a damned rude and abrasive manner. Perhaps he believes that rudeness is part of the moderator's job description.

Mr. Moon points out that chopper-lump assemblies are put together by brazing and then advocates, very strenuously that a rifle be mono-blocked with silver solder. He then makes a blanket statement as to the flow temperature of silver solder.

Not all chopper lump assemblies are brazed. Some are, in fact, silver soldered. Also, the temperature at which silver solder flows, varies from as low as 1040 degrees to as high as 1700 degrees, depending on the alloy and its shape. The liquidus temperature of the average bronze alloy is in the 1600 degree range. Do you see where I'm going with this? You may choose to ignore the potential degradation of the steel's strength at these temperatures, as Mr Moon is wont to do. But think whether you will be able to silver solder those two tubes in, achieve the temperature where capillary action draws the silver solder into every nook and cranny, and be absolutely positive that you don't get things up that extra 200 degrees where the braze joint between the lumps starts to fail? If you can do so you are a far better man with a torch than I am. Someone will say, "Well just clamp the lumps together first". That still doesn't stop the braze joint from liquifying and doesn't ensure that no hidden oxidation and resultant impurities are introduced into that hidden joint.

In answer to your question, yes a threaded assembly is by far the strongest and requires no solder at all. Use the finest possible thread, as the finer the thread, the shallower the thread form and the more "meat" you leave in the monobloc. As an example, the .22 Hornet was built on a .410 shotgun. The thread which I used was .670"-36, which is the tap and die set for the "N"-frame Smith And Wesson revolver. It requires some very careful measuring and calculations to do this though, as you've got to deal with the amount that the assembly tapers from the rear of the barrels to the front of the flats. If you re-read my original post above, you will note that I talked about the fact that this crush fit delivers an almost undetectable finished joint.

Again, my apologies for the mud-slinging. Life is way too short for this nonsense. If anybody has any questions, I can be reached on PM and would be glad to answer. So long all, I leave with a heavy heart as this seemed a damned fine board at first.
Ron Vella.