Contentious issue- that of M16 parts in an AR15. To my knowledge, there is no letter ruling on it. Only a few “I talked to the tech branch” claims.
But, that said, there has been a court ruling that addressed the issue of AR’s with M16 parts (albeit in the context of a DIAS)
[qb]Ninth Circuit- 1995 US v. Woodbridge
The parties present contradicting arguments concerning the
legality of an pre-1981 auto sear possessed in conjunction with
an AR-15 equipped with M-16 parts. Neither party cites any
cases, official BATF rulings or statutes to support their
position. It is unnecessary for us to resolve the issue,
however, because blah blah…
So, to make matters even more confusing, here you have a COURT AFFIRMATION that this very issue (16 parts in a 15) is-
A) Reliant upon auxiliary possession of a DIAS
B) Unruled upon by the BATFE
C) Not cited in the text of any specific law
D) Still in need of resolution
So, neither of you are correct. Barring a letter ruling, someone is going to have to get arrested and taken to trial over it before it is decided.
If you want a letter ruling, just write the BATFE and they will give you one.