I did a lot of performance testing with conicals in a variety of ML's and of those currently available, the Buffalo Ballette performed best "after-impact" but did not perform well on its way to the target at any range. Others like the Lee REAL and Maxi's will sometime group very well yet at a given cutoff point they loose stability and go wild. In most cases accuracy was lost between 55 and 70 yards to the point where at 5-7 yards beyond the cutoff point, you cannot keep them on the paper. Other than the Ballette, most conicals will readily change direction upon impact with bone unless it's a dead center hit on the bone. Using both real and similated bone, some conicals like the Maxi's, Great Plains, PA & BuckBuster will turn as much as 80° off course. Round balls in the same tests deflected less than 15° off course. I started this testing after one fellow claimed he shot two deer standing broadside and found the slug deep in the guts, the other was hit on a front quartering shot and the conical skipped down the side. Another fellow related making a lung shot a moose and the conical exited the chest.
If you're roundball didn't pass-through with 90gr of 2F, there could be several reasons.
Gas blow-by: Patch/ball combo not tight enough or patch failure.
Other gas loss: Nipple hole too large or powder charge not burning completely.
Shooting too far: Round balls loose velocity quickly - shoot within effective range.
On the .50 cal you should be using a 0.490" -0.495" ball with a 0.015" - 0.020" thick patch unless the bore is over/under size in which case you may need to adjust the ball diameter accordingly.
Somewhere along the way something is going wrong unless you're trying to shoot end to end lengthwise. I've shot several deer with .45 cal out to 75 yds and 95 yds with the .50, complete pass-through with both cal's including one with the .50 that took one shoulder joint out on the way in.
PRB's should not be difficult to load either in the field or on the range. A proper patch/ball combo should be tight enough to prevent blow-by but not so tight that it's difficult to load. If you cannot obtain acceptable accuracy until you go to a very tight combo, you likely have a mechanical issue with the bore. If the problem is fouling, you need to look at the lube and load. If you provide more specific, pic's of both sides of fired patches would be great, I'll be glad to try and help you figure out what's going on. I don't make it to the forum on a regular basis these days so feel free to email me direct: [email protected]