doublegunshop.com - home Forums General Discussion DIY Gunsmithing @ doublegunshop.com Forlorn Hope.. Monoblocking

gunman,
There is no need to take them apart, in fact, it is important to keep them together, to maintain the convergence. They should be reamed, while full length( running the tailstock center in the barrel being reamed). Once both barrels are reamed, then they should be cut and squared, to length. New barrels are then soft soldered in, the joint being large enough that silver brazing is not necessary.
Mike

How deep should the joint be? I know a Birmingham trained machinist who may be willing to tackle it.

It'll end up costing a restored Bonehill, but it's worth it. He's a friend, so it's a pleasure.

Regards
Ken

Ken61,
The old barrels should be cut off just ahead of the flats, so that the lugs stay on the assembly. The new barrels will need small flats filed on the side, so they fit next to each other. A new larger hinge pin should be added, so that the barrels can be fitup again. Mike

Thanks Mike.

How about the joint depth? I understand that it would be part of the initial reaming, with the hole diameter for the breech section being sized to fit the outside tube diameter. Or, do the new tubes need to be milled on the joint flange?

Regards
Ken

There was someone who built a double rifle by sleeving barrels into a monobloc, but he used an interference fit. He pulled that off by dunking the new barrels' chamber ends into liquid nitrogen (to shrink them by contraction)sliding them into the monobloc, then letting their return to room temperature do the rest. I can't find the thread but it was fascinating. Avoided soldering.

It's possible, though, that shotgun barrels might be too thin for that to work.

Ken61,
My experience with this was in the shop of a German gunsmith friend, where we used standard tubes that came already contoured and turned to size. Also, I used reamers he had already selected to size and kept at his lathe. Consequently, I can't now recall the diameters, which were in mm, and for 16 ga. tubes anyway. Walther has a website, and on this site shows dimensions of the standard tubes they sell, you could use these for a guide. That part of the site, as I recall, is pretty hard to find( it might be in the German version of the site). I wouldn't try to install them with an interference fit, as suggested above. You would only have one chance to get it right, and would have a heck of a time getting them apart if you made a mistake. I put a barrel in an Anschutz action, that are intended for interference fit. Since it was for a wildcat, I threaded the action, so I could get the barrel out, if I had to. As it turned out, I had to remove the barrel, and wouldn't have been able to do it otherwise. If you make a slip fit, leaving a thousandth or so for solder, and tin both sides, you should be able to get the tubes out if necessary.
Good luck.
Mike

Mike, unless I'm mistaken, gunman was addressing taking the brazed beech joint apart for the purpose of using those separated barrels as donor barrels for Ken's monobloc, which of course would remain jointed.

I myself would be interested in more details about that possibility, especially how applying that much heat to the breech section affects the metallurgy of that critical area.

Ken,
as to the depth of the joint....it goes all the way through the mono block. Sleever tubes are usually turned to the rim diameter. Ellis Brown's (shameless plug for a friend) book on building double rifles on shotgun actions outlines the basics. He threads his tubes for rifle barrels but this is not need for shotgun sleeving.

Vintage barrels were not heat treated so heating them to critical temperature or beyond will not have an effect on them. You do need to be careful with modern alloys. I hate heating up large masses of steel so I would likely look at setting them up in mill and cutting them apart with a slitting saw. It would require careful set up but that is just part of shop life.

Keith Kearcher did a few in the past and they came out very nice.
Did you by chance see them?

Thanks Steve and Mike,

It all makes sense. I must have missed seeing K K's barrels. To do all this, I assume the donor tubes must be separated, fitted into the mono block, then rejoined, regulated, and have the ribs resoldered back on.

Regards

Ken

[quote=Der Ami] gunman,
There is no need to take them apart, in fact, it is important to keep them together, to maintain the convergence. They should be reamed, while full length( running the tailstock center in the barrel being reamed). Once both barrels are reamed, then they should be cut and squared, to length. New barrels are then soft soldered in, the joint being large enough that silver brazing is not necessary.


I was of course referring to the "donor barrels "

As to the method of machining you suggest , let's say it is not the way I have sleeved many hundreds of guns during my working life .