Hi and thank you Jeff,
Let me elaborate a little that may help you. You can simply solder a sight with a wide base on the barrel. That is authentic and common on cheaper guns. Since I focus more on higher end guns, I mortise sights like the one I showed in two different ways. On barrels with really thin walls at the muzzle, I cut a very shallow mortise and then solder the sight in place. Those sights usually have very thin blades. Here is an example.


The barrel for that gun is one of Rice's "Dolep" barrels made from 4140 steel. We cut a narrow trench for the sight, which also had a pin filed on the bottom. That pin actually stuck out in the bore of the barrel and was polished flush. That is not uncommon on original English guns. The sight was soldered to the barrel using StayBright low temperature silver bearing solder. On thicker walled barrels, we usually mortise and then solder those thin front sights. With the wider, more massive front sights, we file the sight from sheet brass or silver and then use a jeweler's saw to cut a fine groove all the way around the base of the sight. We cut the mortise with a flat chisel and undercut the edges just a little. Then we peen the barrel around the sight using a punch and that groove accepts the peened steel of the barrel, firmly locking the sight in place. Here are several more examples done that way.


Then there is a much more complicated solution found on the best pistols and sporting guns, the spider sight. The star shaped sight is cast with the front sight or the sight is rivetted to the silver base. The barrel is chiseled to accept the base and the edges of the shallow mortise are undercut.


The silver is then peened to spread it into the undercuts and lock the sight in place.

I learned that work on my own with no one to show me the way. I can only say, doing that on a barrel for a gun I put in over 300 hours worth of work was stressful to say the least. Anyway, it was a common technique on good quality guns and I suspect the young kids who did it back in the day could do it in their sleep.
dave