Pretty much any aged bison's horns are soft around the base. The tough part is that the horn caps are attached to the skull like the ends of an axle shaft or end of a drive line, with splines. They are heavily ridged on the inside and form an exact fit over the skull. You can still successfully boil and remove them. Here's what I do...
1) I cut the circumference around the base where the horn ends.
2) I cut the flesh away from the horn base and cut up under the horn as far as I can get. It won't be too far, however. Just anything to help the hot water get in there.
3) In order to keep the horns from flaring out too much, I then use electrical tape and tape quite a bit around the horn base. After the tape, then I tightly tie wire around the base. All of this in order to keep the horn in tact during initial boiling. I use this same process with pronghorn skulls. Works slick and quick.
4) After boiling for a couple/few hours, the membrane between horn and bone will cook and soften. Although it still takes elbow grease, I usually kneel on the center (forehead) of the skull and twist (hard) till the horns pop off.
5) I then leave the wire and tape on for a day or so. I also fill each horn with Borax right away and leave it for about a week.
6) Then just continue to boil till you see the results you are looking for.
Here's one from last year. You can see the white fleshy bits at the base of the horns and the nasal turbinates you want to try to preserve.
If you would like to borrow any of my cooking hardware (pots, burners), feel free to PM me.
~ Best of luck.
