I've used Permalyn on recent gunstocks and I'm very pleased with the results, especially sealing the wood. Some pistol stocks and several knife handles.
I've used shellac previously, but water can get under it, even when covered with polyurethane, turn things may turn brown/ugly.
Permalyn is good for gunstock & knife finishing. I've also tried their dyes for antiquing horns and found them useable.
I don't know what the long term issues may be vs. using RIT dye to age a horn. Maybe both/neither/all will induce a horn to crack?
Maybe beeswax is the best over time?