Just ordered mine tonight. 4.5" with ported end. Should look awesome. Will definitely get more looks at the range than I already do. I get asked a lot about whether it's suppressed....now they won't believe its not...also will give an appearance of SBR. Check out the two Youtube videos:

Muzzle Brake / Fake suppressor made on a Biglia CNC - YouTube

Over barrel shroud - YouTube

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M&Ps 40C, 40FS, AR15 Piston