I see M16A1 parts for sale in original parts kits.

I'm guessing the FA sear doesn't ship with those of course.

I know the bolt carrier, trigger, hammer, disconnector, and selector lever all differ on the M16 vs the AR15. All those parts are fine to have on a federal level.

WA state however has:

https://app.leg.wa.gov/RCW/default.aspx?cite=9.41.190

It is illegal to:
"Manufacture, own, buy, sell, loan, furnish, transport, or have in possession or under control, any part designed and intended solely and exclusively for use in a machine gun, short-barreled shotgun, or short-barreled rifle, or in converting a weapon into a machine gun, short-barreled shotgun, or short-barreled rifle;"

I know plenty of places in WA sell the FA BCG, as some people prefer the heavier version.

But what about the original M16 trigger, hammer, disconnector, or selector lever? Are those legal in WA or do those count as "machine gun parts"?

Just my opinion as I am absolutely no expert on the subject.
I believe full auto is grossly over-rated.
I tried it down in Las Vegas last year and I couldn't hit anything with it beyond 25 yards.
Definitely fun, but very limited usefulness outside of burning up a lot of ammo and making noise.

I believe it is fine to possess a full auto bolt carrier, that's about it.
FA bolt carrier is better simply because it is more robust.

You'd be much better off with a match grade semi-auto only trigger in my opinion paired with a quality barrel and a proper scope or red dot sight.

Recommend you contact an attorney versed in firearms law.

Everything except the bolt carrier is questionable, even federally.

I wouldn't touch FA FCG parts here in WA state. (M16 "style" bolt carrier being the exception)

The context of a potential "violation" means as much, if not more than, the letter of the law, but "any part designed and intended solely and exclusively" is a pretty clear and high bar.

Like I said in the other thread, usually the vendor doesn't ship the parts they know are verboten.

WhatACountry has a note on their pages saying they will remove pieces depending on your ship to address. The last kit I ordered from McKay had all of lower parts but not the auto sear, so I ground down the trigger parts to make them semi-auto only.

Just grind off the bits in red.

Colt's ship with an auto carrier and hammer these days. Just say'n.

I have yet to see a Colt ship with an auto hammer.

If you have a M16 full auto trigger you can be hit up on intent to construct a MG.
Lowers with a sear hole is a big no no too.

BCG is not consider a MG part so don't worry about the BCG.

The RCW is pretty clear on possessing parts designed for full auto and would include a BCG if they go by the letter of the law.

https://app.leg.wa.gov/rcw/default.aspx?cite=9.41.220

If 90% of all the AR's use an m16 profile BCG I wouldn't say its intended solely or exclusively used for machine guns.

RCW 9.41.220
Unlawful firearms and parts contraband. (Effective until July 1, 2019.)
All machine guns, short-barreled shotguns, or short-barreled rifles, or any part designed and intended solely and exclusively for use in a machine gun, short-barreled shotgun, or short-barreled rifle, or in converting a weapon into a machine gun, short-barreled shotgun, or short-barreled rifle, illegally held or illegally possessed are hereby declared to be contraband, and it shall be the duty of all peace officers, and/or any officer or member of the armed forces of the United States or the state of Washington, to seize said machine gun, short-barreled shotgun, or short-barreled rifle, or parts thereof, wherever and whenever found.

I wouldn’t even go down that round with a f/a fcg. Just not worth the risk.
Legally, I don’t believe there is any question to what those (fcg) qualify as. Parts to a mg. The bolt carrier is a totally different animal since it’s just a profile used to designate mil vs commercial, not an actual f/a part.
Really there are two different legal aspects you need to be aware of, letter of the law as written, and intent.

If you ever have the unfortunate luck to be face to face with an atf agent or LEO who is inspecting your guns and spare parts, is it even worth trying to explain why you have parts or a complete trigger group for an m16? Installed or not?