Is this a Pedersoli Rocky Mountain percussion Hawken we are discussing? I suppose a conversion
could be done, but I don't know of a kit made for that purpose. If such a kit existed, it would probably include a new lock, barrel with breech installed, and a new tang with standing breech for the hook. Pedersoli's guns are not cheap, but their parts are astronomical. A permanent conversion would at least require rebreeching and a new lock. I don't know of a flint lock that would fit that lock mortise "out of the box." I think this job would be a real chore, best done by a professional. It won't be cheap, and in the end, you'll end up with a rifle unlike any
known rifle from history. I honestly don't think you'll save any money, and I doubt you'll be happy with the result. In addition, I have no doubt a conversion like that will seriously devalue your rifle if you should ever want to sell it.
If I may make a suggestion, and you think you'll be happy with a halfstocked Hawken-style flintlock, maybe trade your Rocky Mountain Hawken for one of the new Lyman/Pedersoli Great Plains Signature rifles in flintlock:
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Your Rocky Mountain, in new condition, is worth more than one of these. Used, you might make an even swap or even spend a few dollars, but I think you'll come out ahead in the long run. These Signature GPRs are said to be very nice rifles.
Mr. Kibler's kits have gotten a lot of press lately. By all accounts, they are excellent in every respect. However, there
are other builders still out there, and I think it would be to your advantage to research it some more and determine exactly what you want. You might just find a used flintlock that fills your needs for a reasonable price, and you keep your Rocky Mountain Hawken intact.
Good luck to you!
Notchy Bob