This is the first Sig i have owned so I could use some help. I have read a few people talking about changing the barrel out on the P226 .40 and you have a .357 Sig. I asked the Sig rep and she was saying i had to buy the exchange kit, she would never say yes or no just to buy the exchange kit. Is that all there is to it, just change the barrel and you're good? You dont need new magazines, or change out the recoil spring?