This year Smith & Wesson have launched the M&P15 PS and PSX piston operated AR-15 rifles.
The only difference between the PSX and PS is that the PSX features a Troy 7″ modular quad rail handguard.
M&P15 PS model and Piston Operating System
Photo ⓒ Remigiusz Wilk (REMOV). Used with permission.
Barrel Length: 16″
Barrel Twist: 1 in 9″
Overall Length: 35″ Extended/32″ Collapsed
Stock: Collapsible 6-position
Weight: 6.5 lbs.
Finish: Hard Coat Black Anodized
I do not know the MSRP on either model.