What's the opinion on building a 16 incher in 9mm with a lower that was bought a week ago.

Its not mine, I would build an sbr since I have a trust.  

My buddy really wants a 9mm and does not want to hassle with nfa.

I have been doing all sbr's since the law changed and have never really thought about it.

My only issues that a Colt 6951 9mm can be had for $1,200.  Hard to build one for less than that.

Sorry guys got busy yesterday.

The issues I was thinking about are not being hbar. Had I gun store employee suggest it was not legal because it's not hbar specifically. I think it's not .223/5.56 so it's not a copy cat. If the colt is for sale then it's legal in MD so that answers that.

He is using a spikes worthogo billet lower, so no prebuilt for this project.  It's his money, he is not heavy into ar's it's the only one he plans to ever build. Until the disease get him lol.

9mm is blowback, which is not an AR-15.

If a pistol system makes it no longer an AR, then removing the gas system completely absolutely does.