The M&Ps are strong pistols so as long as you shoot quality ammo through it I wouldn't worry. Nato 9mm such as Winchester or Federal are slightly hotter than non+P ammo and perfectly safe in any M&P including your Shield. Smith & Wesson and any other manufacturer will tell you that the use of +P ammunition can hasten wear to your pistol and S&W recommends against using +P+ ammo in any of their pistols. For practise I shoot mainly Federal 147 grn FMJ because this is the weight of my preferred carry rounds. Many prefer +P ammunition for carry and non+P for practise. Whatever you put through yours it's unlikely you'll ever wear a properly maintained pistol out. These M&Ps are tough.