Sounds like you got one of the
CVA Squirrel rifles. You are going to get a list of various shot-strings and they will all be in the ball park. This is why you then will have to put in some range time and come up with "your" optimum load. Regarless, stick with the FFFG.
As mentioned, the rule of thumb is that the Min propellant load it 32 and the Max, is 64. .....
Be Safe !!!