It is really difficult to say what will shoot best in your rifle. If you and your dad have the same rifle they may shoot differently. That is just one of the things you have to deal with. I would expect the powerbelts to shoot well and I would stay at 100gr of powder or less. I would recommed that you start with 75 or 80 grains to start and work up in 5 grain increments for best results. If you do not want to spend the time just settle on 80gr which seems to work in every rifle I have shot. Let us know what your rifles are and the results for them may be easier to predict. What Powder are you using. Pyrodex is a good starting powder although there are newer synthetics and real black powder is good too. Pyrodex is just easier to get and an old time standby. I will try to help more if you want.