Stick with the lighter loads in your gun. It really isn't built for a steady diet of rhino-rollers! :hmm:
And you shoulder probably isn't either. That is a light gun which is why they are so treasured. Treat it nice.
You can calculate the maximum efficient load that will burn in your barrel length by using the Charles Davenport formula for Round Ball loads of 11.5 grains per cubic inch of bore. A 28 inch, .45 caliber will burn a little more than 51 grains of powder, behind a round ball. Drop it ten percent to get a more accurate load.
When you are shooting conical bullets in these guns, the added weight of the bullet, and the additional friction caused by the wider contact surfaces of the bullet against the lands will increase barrel lag time, and increase chamber pressure. That in turn will burn more powder efficiently than what you shoot with a PRB. You may be able to burn up to 60 grains of powder, depending on the length and weight of the conical you use. But remember, both the weight of the bullet and the weight of additional powder ALSO contribute to greater recoil forces. Its one of Newton's laws, and we can't change that. Put that all in a light rifle, and you are going to notice the recoil.
So, IMHO the best thing you can do is be nice to that gun. I did a lot of good shooting with a 25 inch .45 cal. barrel shooting just 45 grains, at 50 yd. targets. The 30 grain charge was accurate at the 25 yard targets. I know a gunmaker who just finished making himself a short deer rifle with a fast, 1:14" ROT barrel for conicals, and he is using 28 grains of FFFg for his load. He is shooting one hole groups with it at 100 yards, and the penetration testing of that conical shows its more than adequate to kill a deer. He does not expect to shoot a deer at that distance, as he hunts in heavy brush. The barrel is only 16 inches long, BTW. I believe the velocity is in the 1200 fps range at the muzzle, and is still more than 900 fps out at 100 yards.
Now, don't expect that kind of performance shooting a PRB! Instead, expect any PRB load to lose 45% of its MV at 100 yards.
Most of your shooting will be plinking and short range target shooting, so just shoot the PRBs and go have fun with that nice gun. You are not going to regret buying it. :hatsoff: