Underlug attachment

[Nordnecker]

How do you think this was attached?

[James Rogers]

The ones I've inspected were slightly undercut on barrel to hold for a brazing.

[Nordnecker]

While waiting on responses today, I might have answered my own question. The photo actually reveals more than what I saw on the original gun.
I thought convention dictated dovetailed lugs on an octagon Bbl and soldered lugs on a round. When I first saw this, I thought it was staked.
So, I decided to try to dovetail a lug into a round piece of pipe. It worked. The base was only about 1/32 thick, but when filed flush with the "barrel" it left a shadow like the picture above.



This what the other side of it looks like. I realize that the thickness of the barrel wall needs to be considered. Before I do this on the actual barrel, I will thin down the base of the lugs a bit more.
Why not just solder them, you ask? Well, That's not how the original builder did it. It isn't often we get a peak at the inside of an original.

[Acer Saccharum]

The lugs merely hold the wood to the barrel.

You can chisel a pocket for the lug flange to drop into, and raise the edges of this pocket with a small chisel. File the lug to fit into the pocket, leaving tapered tapered edges on the flange of the lug. Once the lug is in place, tap the edges of the inlet down onto the tapered edges of the lug base. File all around flush with the original barrel surface. Use small chisels, and you will avoid dimpling the bore. Works great with thin wall tubes.

[Acer Saccharum]

If the above scares you, then solder the lugs to the tube.    Just conform the base nice and thin before you solder. Tin both lug and barrel before soldering.

Take a piece of steel wool and scrub the barrel with flux and solder as the heat rises, and you'll get perfect solder flow on the steel. Do same with lug. Once both parts are coated, clamp together with flux and gently heat until solder melts; add a touch of solder to fill any gaps.

[Nordnecker]

Thanks Roger and Acer for responding. I don't want to come across as one of those people who ask for advise and don't listen.
I was not aware that dovetailing into a round barrel was normally seen. I expected to see lugs that were soldered. It looks obvious from the above picture that it is dovetailed. I just wanted some other's opinions- a little reasurance that what I thought I was seeing made sense.

[Acer Saccharum]

Be wary of pounding too much on a thin-walled barrel. Big chisel = heavy hits.  Small chisel = many hits, but little chance of depressing the bore. Sharpen the chisel so it functions at a low angle, then the driving force is mostly horizontal instead of downward.