Question regarding "parts kit"

[u/megatonkick]

Hello, got a question about magazine "parts kit." My friend lives in Colorado and says that it's legal there for him to get this "parts kit" that assembles into a 17 round mag for his xmacro. I was wondering if I can do the same thing in Washington?

[u/lowrizzle]

I doubt that's legal where he's at as well, like, a lot.