In the case of tap loading fixed barrels, it did not quite go as they thought. Yes the barrel is permanently aligned with the sight but the tap has to be perfectly aligned at assembly. It rarely is. Most manufacturers had a pretty good stab at getting it right but the shear aspect of limits and fits means it can never be perfect. However, the later use of fixed barrels with sliding breech covers, like the HW77/97 got around the problem with the best of both worlds. This system has to be potentially the best behind bolt loading PCP.
Its actually quite a tall order to beat a high quality break barrel, where pellets are seated with the best possible tool yet invented..your thumb!