I have a couple of questions; what Bess lock is this? Pedersoli, TRS, recent India make, etc. I have used a pedersoli Bess for 12-15 years and have two other extra locks I swap in and out. These locks have had thousands of shots fired and I have only had to harden one frizzen. When I did this the first time I used a small rivet forge and actually over-hardened and eventually with use broke the base of the frizzen. I then picked up another frizzen and used Kasenit with great success. I have since done a couple of friends Bess frizzen and had no problems. I have built a couple of TRS muskets, 1740 Potzdam, etc. and cast springs and frizzens can be a challenge to get right if you don't know what you are doing.
JAS