Sidro, to switch a P14 or P13 (.45acp) to a .357 Sig you need more than just a barrel. You would need a P16 (.40S&W) slide (has correct breechface for .357 Sig) and a custom .357 Sig barrel (BarSto has them for Para Ordnances) and you would have to swap out the frame mounted ejector when switching between .45 and 357 Sig. Its really not cost effective to build a switchtop gun with calibers that need a different ejector. For the price of the slide, extractor, firing pin, firing pin stop, series 80 parts, barrel, bushing, sights and ejector you could buy a very nice gun in 357 Sig. It would be much easier to convert a Para P16-40. good luck