I don’t own a single lower that was purchased as a complete rifle, and only one has ever had a rifle length barrel mounted to it. I have a Quarter Circle 10 9mm lower that was built as a pistol years ago with a 10” barrel and Phase 5 foam covered pistol buffer tube , and I researched it back then but forgot the details on why what I built was OK. I also have a lower with a pistol brace with a 9” .22 lr upper attached to it, and it has never had another configuration. I’m currently in the market to build a 10.5 .223 upper, which is why I’ve been perusing the AR pistol threads.
I was not aware of the forward grip being a consideration. Fortunately, none of my short barreled uppers have ever had a forward grip mounted on them, although I had the desire to do just that. I’m glad that I asked the question or I could have found myself in some serious trouble.
Honestly, I think that this is the year that I break down and register 2 of my lowers as SBRs so that I can put proper stocks on them. There is a part of me that thinks that if the Dems win in the upcoming election and go after ARs that maybe, just maybe, tax stamped/registered arms might be exempt because they are registered and have extensive background checks done before issue. That may be a pipe dream, but who knows.
Lou