I've offered this thought before but feel compelled, with all due respect, to offer it again. The "thought" - maybe even a fact - is that for prb, there is too much importance put on the "rot". The main consideration is groove depth with rot coming in second. A fast twist will stabilize a prb if the grooves are deep enough; but there is a limit to the rot, obviously. In general, conicals do not like deep grooves and work best in bores that have shallow grooves. In shallow groove bores combined with faster rot, a prb will "skip" the rifling with anything other than powderpuff charges. But conicals, on the other hand, can easily bump up to ride the shallow grooves for good accuracy. For a prb to do well in barrels with shallow grooves, the prb needs to be rather tight, either by using a larger ball or perhaps a thicker patch. This is just my observation over the decades; I am not, even remotely, an authority.