It would represent an tremendous effort & expenditure to develop jacketed bullets that would perform as good at .22LR velocity as the standard lead bullets we now have. It simply would be damn hard to make a jacketed bullet expand. The jacket would likely be as thin as some of the current coatings, or "copper washing". I really see no problem in the different lead bullet loadings as not only do they remain very inexpensive, but also almost impossible to wear a barrel out with modern steels with lead bullets. Yes, it's true the rifling designed for jacketed bullets only MAY be slightly different than rifling designed for lead bullets exclusively, but by the same token, then that barrel wouldn't perform as well with lead bullets-in theory.