I have no personal experience with your rifle, but if I owned it...

Clean the devil out of the barrel first. Remove all traced of any oils, bore butters, and alike. Always start on a nice clean barrel. Pop a 209 primer through the breech plug and blow that clean.....

I would start my testing at 80 grains of Pyrodex FFG or Triple Se7en FFg. Before you shoot a powerbelt, remove the plastic button on the bottom. You will see a little lead spike on the conical. Put a drop of oil, bore butter, spit, what ever and replace the button. (this is especially important if your shooting Triple Se7en because of the heat the ignition causes) Then load as normal on the powder charge. Shoot a three shot group. If the group is tight then increase the powder charge 5 grains and shoot another group. Keep doing this until the groups falls apart. I will guess the rifle will come in around 90-100 grains. If you're shooting pellets, then load two 50 grain pellets. Powerbelts out of some rifles, do not like to be pushed too hard. Do not exceed 100 grains of loose powder with that rifle. Especially Triple Se7en. You are getting some high barrel pressues with those heavy conicals..

Be sure and swab the barrel between shots even though the powerbelts are slip fit. You are sighting in trying to see what the rifle likes. After you have you load then you can try shooting a couple in a row without swabbing and see what it does. I use a mix of 50/50 isopropyl alcohol and car windshield washer fluid. I run a wet patch working in short strokes from the muzzle to the breech. Turn it over and run the whole length of the barrel, then a dry patch or two (they are my next wet ones).

My rifle likes 90 grains of Goex 2f and a 245 or 348 grain powderbelt. It will shoot outstanding groups. It is not a Beartooth or Optima but it is a CVA Staghorn.. from the same family.

Good luck with the rifle. Others I have read are shooting 240 grain T/C Mag Express XTP's with 85-100 grains of powder with excellent accuracy.