I have not purchased a 340 yet. I was looking at the M&P. Looks like a good gun. I checked out the ballistics of the Speer SB 135 Gold Dot and it sure looks like a good choice as far as 357 Magnum ammo goes. My biggest concern with a 340 and 357 Magnum ammo is pullet pull. I think I would go with the Gold Dot 135 grain 38 Special +P. This load works well for the NYPD.