Heating a frizzen to 650 degrees is not hot enough to harden. The critical temperature of 1450-1550 degrees must be reached to harden 1095 steel...IF the frizzen is indeed 1095. In my experience with a Petersoli bess, the frizzen may not be hardenable steel, and will need case hardening.
In my experience, it takes more than a single propane torch to heat a part to critical temp. I'm told that MAPP gas will do it, but I have never tried it.
The best way for someone to harden a frizzen without a forge or acetylene torch is to pack the part in a pea size lump charcoal inside a tin can. The charcoal should completely fill the can to within an inch or so of the top, and completely surround the part, with a minimum of a half inch of charcoal between the part and the sides of the can. The space at the top of the can should be filled with sand to prevent oxygen from reaching the part. The sand allows excess gasses to be vented off without oxygen getting to the part.
The can can be completely filled with charcoal if you don't have sand readily available.
A lid, or metal plate shuld be loosely placed on the top of the can, loose enough that it will fall off of its own weight when the contents of the can are dumped into the water quench.
Build a hot fire in your BBQ grill and rake out enough coals to surround the can. If you are using lump charcoal, get the charcoal going good, and carefully rake it around the can to the top.
Keep the coals going for at least an hour and a half. The can must remain red hot for a minimum of an hour, longer is better.
Dump the entire contents of the can, frizzen, charcoal, sand, lid and all into a 5 gallon bucket of hot water. Be careful here. Do this outside, 'cause hot charcoal ash will fly all over the place, as will hot steam. Wear safety glasses, a hat, and preferably long sleeves, and use the longest tongs, pliers, or whatever you have to handle the can when dumping. And Dump the can upside down, so all of the contents go into the quench. Don't let the part be exposed to the air longer than necessary. The can doesn't go into the quench, BTW.
Oh, it's a good idea to dampen the hat.
The charcoal does not have to be packed real hard just moderately. Charcoal does two things. It keeps the oxygen burned up that enters the can and also forms a carbon rich gas in the chamber. Iron has an infinity for carbon and the iron will adsorb carbon to a depth of about .010" pr hour at 1500 deg. F. Carbon can be absorbed it at lower temperature but a lot slower. It should be no lower than 1250 deg. F. to absorb carbon. Parts quenched below approximately 1400 degrees will not harden. Parts need to be quenched at 1500 degrees to harden well.
If you are in doubt as to whether the part is mild steel or tool steel, quench it in 130 degree oil or at least put a thin layer of light oil on the water. About a 1/16 inch layer of oil will do.
When the part cools, try scratching the surface with a file. If the file skates across the surface, the part is hard. Now, go into the kitchen and place your part in the oven at 350 degrees, for an hour and a half. The part needs to remain at 350 for that hour, so leave it in a bit longer. Longer won't hurt.
Most thermostats on kitchen ovens aren't very accurate, so it's a good idea to use an accurate oven thermometer, if you happen to have one.
When the frizzen has cooled, heat the toe and tail of the frizzen to a full blue color with a propane torch. Run the blue color up the tail, through the toe, and part of the way across the bottom of the to the edge of pan cover.
Be sure to heat this area to a full blue color. Frizzens often break at the joint of the tail to the pan cover, or at the screw. Tempering this area well will prevent breakage.
The heating element or top burner on a kitchen range should work to heat the tail and toe, though I haven't used them.
The frizzen should now be good for quite a few shots.
J.D.