Originally Posted by cyphertext

Yep, an "updated" model. The 15x used to come with Troy goodies... now it has the 1:8 twist, 5R barrel and S&W branded hand guard. Kinda like how the 15T was "updated" a few years ago. S&W considers the 1:8 twist, 5R barrel to be a premium barrel, and are putting it in several of their models. It isn't going away, just not being used in the Sports.

Here is a link to the older version. M&P(R)15X | Smith & Wesson