I think that we agree that there were many methods of making horns then and are many ways to make them now. This makes the working of horns more interesting and justifies having a collection to demonstrate these types. At least, this is what I tell my wife.
There are different opinions regarding how the majority of powderhorns were produced in the ML period of history. Some think that the average woodsman made his own and this may be true in some areas and time periods. Plugs fitted to the unrounded butt are found and few (if any) shops would do this as it is labor intensive to shape a wooden plug to an irregular horn compared to reshaping the horn and then lathe turning both. There are also complex horns which no woodsman could have accomplished with his files, knife and scrapers. Then there are significant records regarding shops turning horns out (pun intended) in great numbers.
So we see two fundamentally different powderhorn producers using very different processes. The best advice is to study what you are trying to reproduce in a good faith manner and honestly communicate what it is and how it was done.
My particular interest is in recreating the manufactured horns of the various times and regions which compliment the guns made in those times and regions. I like to see a correct gun and horn as a matched set.
These particular horns generally followed set patterns of production. They were done in stages - sort of an early version of assembly line production, but not necessarily with interchangeable parts. Many still have the production numbers inside to keep the components matched up together. (My horn making buddy does his in batches and uses a similar numbering system ”“ partly out of tradition and partly because it helps in keeping the items together in a confusing environment where numerous horns are being made at one time.
Having seen original horns disassembled, there are often bent staples in the butt plugs and bodies. Sometimes there are also materials sealing the holes and sometimes not. I have no problem sealing the holes with period or modern materials. The horns should work properly and as you say, if it is not visible, it does not really harm anything. After all, this is intended to be a functional container for outdoor carry of black powder. We can do pitch, hide glue, wax, marine glue or epoxy as deemed advantageous. You decide for yourself or ask your customer. How far do you want to go in the period correct realm? I am not walking to Dixon's, but I might use bees' wax or hide glue as my insurance for making a horn water-tight. I have also used epoxy. You would not know the difference unless you asked or it had been previously discussed.
Far from simply relying upon modern electronic media, I have read and referred to books. I also examined originals from a couple of collections. My favorite source is Art DeCamp's Pennsylvania Horns of the Trade (Screw Tip Powder Horns and Their Architecture.) I have also visited his exhibit to see the displays and discussed these horns with him. My horn making buddy has taken Art's classes in making the Philly applied collar internal screw tip and Lancaster screw tip horns, so I am learning from both of them.
A momentary break from the reading:
Here is the neck of an Adams County horn that I did a while back and use for display at events:
The tip was patterned from one in Art's book.
The butt is a blend of a copy of an original in a collection here in Mississippi with some additions from Art's book. It is helpful to make a reproduction while holding an original of that type, but the book is so good that it is almost as helpful.
The wire staple in the butt on the original was straight as suggested above. It did not come through the wood and was therefore not bent over. But I chose to bend my recreation because I thinned the butt to lessen weight and increase the volume of powder that the horn can carry. Not completely correct, but it does not show...
The wire in the neck of that original was not visible, but the wire was so thin that I bent my copy over and sealed it with carpenter's glue inside to make sure that it would not come loose or leak. The neck was so thin that I cannot imagine the staple of the original not bent over.
The Philly collar screw tips were held in place by wire which could be a rounded arc or a sloping angle and I was told to bend them over inside to prevent them backing out. There is not a lot of stress on them, so I could see either way on this. I reread Art's book, but could not find this item addressed specifically. The opening is so wide that this can be seen on most - will need to look when I am back in the shop. There are several originals there. Styles with smaller openings or deep bends are not as easily visible.
I think that the original discussion involved the staple in the neck area. I am not certain of the data involving percentages of horns bent over or simply driven into the horn. In seeing my buddy's collection and at Dixon's, I have seen both ways, so the comment of making it how you like might apply in many cases.
As to the wooden butts, several originals were clearly bent over inside the wood butts when the wood was thin - Art's book has examples where they were bent over. EG - Page 254. As you mention, some were straight. Page 254 is simply driven into the wood which is quite thick. The technique of turning seems to drive this choice. Some styles were not chucked on an internal pillar at the inside so the wood remains thick. This would require a very long wire, so it relied upon the straight staples to hold.
In some styles where the inside of the wood plug was thinner and/or an eyelet was used, the ends of the wire were pushed through the same hole and twisted together before being "clinched" (As Art terms this bending) on the inside. Art had this on his table the year before last.
Here is a Philly with a wire eyelet which uses one hole to secure the bail. It is correctly secured internally by a bending or it would surely come loose in use. It is also sealed since to two wires would not provide a watertight fit.
Art teaches this and has examples to demonstrate how the turning was done and the wire was twisted.
In short, there are many ways to do a correct horn, but the actual practices of original shop produced horns of the trade are a bit less flexible. They follow the practices of the particular shop so you would do well to study if your intent is to reproduce these.
I strongly suggest this book for any people who wish to make the shop built horns of the era. It is quite a good reference. Art's classes are also well regarded. I just need to retire so I have the time to attend!
CS