Questions for Swashbuckler and Feats

[The Genie]

Ok so if you crit on a Pummeling Style attack once you multiple the total damage by your crit multiplier. But what if you are attacking with a weapon that has an improved critical threat range like 15-20/x2 like a rapier in the hands of a Swashbuckler.

So say at level 6 I make a pummeling style attack and I crit on both attacks Do I increase the damage by x4?

Is the kukri a valid option with Slashing Grace? Would Piranha Strike be better then Power Attack for this style of Swashbuckler?

[Ascalaphus]

This comes back to the question of what weapons pummeling style can be used with. If you look at the table summarizing the feats on page 140, you'll see that it probably only works on unarmed strikes. (This is an ongoing controversy.)