The Surefire option will probably serve you well - the 556k is a 6" can, and there's even shorter versions that cut an inch and an ounce off the weight - down the road those make a lot of sense, along with an AAC M4-2k, Gemtech G5, or the KAC NT4.
Based on what you have right now though, you might do well running a 14.7"/14.5" unit with a pinned hider, and then either shorten that or use that upper for a time until you have a suppressor, then run a new upper with it.
A Title1 lightweight upper will handle as well, with the exception of the weight issue.
I suggest this since I've decided to give this route a try - making a 14.5" A2X lightweight, while I'm accumulating parts for a 10.5" suppressed unit that will be set up identically except for barrel (Both VTAC Extreme 9.0 HG, X300 at 12:00, DD Front Sight, AFG, Aimpoint H-1 and MBUS Rear)
عندما تصبح الأسلحة محظورة, قد يملكون حظرون عندهم فقط
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Semper Fi
"Being able to do the basics, on demand, takes practice. " - Sinister
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