Not at all John. Using oil I should have explained more, but thought I already explained that in another thread. My bad.
Anyway, cow and bison horn are similar in characteristics and armed with that assumption I keep my oil in the 340 - 350 degree range. I use a candy thermometer to get to that range that's the temperature I'm told is the range in order to get the horn to 'forget its memory', to put it simply.
And the thinner the rim area is scraped the less time it will need to be dunked in the hot oil. When I start seeing an even pattern of 'bubbles' rising to the surface I will take out the horn to test for pliability. If okay I insert the sizer and let it cool, but if not then re-dunk for a few more seconds. What ever you do, don't over do the time or you will get potato chips.
Secondly, most/all the bison horns I've worked were not terribly 'oft round' to begin with so to get a plug or sizer to 'finished round' can be done easily with boiling water where the oft round bison wasn't going to seriously be in conflict (read cracking later) with the now 'round' butt plug. If your bison horn isn't terribly deformed like this example then maybe the boiling water method, which is neater and cleaner, will fit your needs.
Gary