Well, that will fit the bill then, though I wouldn't call the M&P10 light. It's a good rifle but not light, no .308 chambered rifle is.

It depends on your priorities but an AR15 with a 14.5" barrel with a pinned muzzle device or a 16" barreled rifle might be better for the lightness factor. I'm not dissing the rifle, I love my 18" model but 2 inches less on the barrel isn't going to make much of a difference in weight. If you plan on using it for hogs or something that needs a heavier bullet, then the M&P10 might be the best choice.