Sorry! I just read this thread and getting a little slow on come backs. Thanks for the kind words.
My take on burning spout holes is this. If the powder horn was made by someone at a farm, homestead etc., who didn't have a hand drill. Burning a hole with a red hot wire probably was more common. In my earlier years of horn making, I tried this on a couple of cow horns to mainly see if I could do it. I did with mixed results. I did it the way I DRILL the spout holes in my horns today. I use a coat hanger wire and bend it to the general curve of the horn. I then stick this wire into the horn to measure the interior cavity depth and mark the wire at the big end of the horn. I will then take the wire and hold it along side or the horn and mark the tip end of the wire where it stops. This is the depth of the cavity of the horn. From the mark that I just put on the horn at the end of the wire, I measure about an inch to an inch and a half and make another mark, then cut the tip of the horn off at this mark. This is the straight short area of the horn that you burn out or drill. Mark the center in the horn end and drill slowly watching your alignment. It doesn't matter how thick the spout end is, as you have to scrape or file it down anyway. In the many gun shops and horn factories of the 18th Century. Most if not all of the spout tips were drilled not burnt. Remember, Not everybody was a Blacksmith to forge drill bits and files were very expensive and the average Farmer or Homesteader probably wouldn't of been able to afford such a luxury tool!
Tapers: Tapering a spout hole is easily accomplished by using the tang end of a file as a scraper.
Hope this helps,
Rick