That is a hard question to answer because a lot of it will depend on the rifle itself. I own six different inline rifles and they all seem to like something a little bit different. What one shoots well the others do not. IfI had to suggest bullets to try that would probably shoot well;

for the .50 caliber

240 grain Hornady XTP
300 grain Hornady XTP
200 grain Shockwave/SST
250 grain Shockwave/SST
300 grain Shockwave/SST
250 grain Barnes Expander
300 grain Barnes Expander
260 grain Nosler Partition
300 grain Nosler Partition
375 grain Buffalo Bullet SSB
245 grain Powerbelts
295 grain Powerbelts
348 grain Powerbelts

as for what powder charge, that would be impossible but they should range between 85-120 grains of powder depending on barrel length, among other things....