help me build!!!!

[surfj9009]

ok, please bear with me as I am new to whispers and I am typing on an iPhone right now. I have a Grendel for precision work. I live in WA so no SBR! I want a supressed whisper. I want it as compact as possible. WA allows a minimum 16".

So I think if I want it short and suppressed, I will have to do a integrally supressed barrel. This will be for my AR by the way.
Now I know there is a lot if talk about gas port placement, but I have not seen it addressed on here for an integrally supressed rifle.
Here is where I need help, as much of this build is new to me:
if I have my own upper preference (HPI Rifles ,match with a side charging handle), all I need is a barrel and a machinist to do the integral supressor right?
So... In order to keep it at 16" what size barrel would you guys say is the minimum for a subsonic whisper only, and can anybody recommend a barrel/integral supressor/machinist combo for what I need?
Remember, this does not need to be a match rifle, so I can deal with lower costs for not having the best barrel/machine work. I did that with the Grendel.

So please help!!!! I want to build this baby and do it right. I need more help than what I have found perusing the threads on here. I have found nothing similar to what I want to do, so let's get some great ideas going on here. This will be a sweet project when it gets built. Please remember that I want it as close to "no shorter than 16 inches" as possible. :)