Will converting a pistols cal. decrease it's reliability.?

I was considering converting a .40S&W Jericho 9/41(a.k.a. Baby Eagle) into .357 sig. The Jericho is a very reliable handgun and I'm somewhat afraid of making at all more prone to jamming. I admittedly know relatively little to the internal operation of pistols and wanted to make sure I wouldn't mess the piece up.