Incorrect. Any lower transferred as “other” can be built into either a pistol or a rifle. Doesn’t matter if a stock has been put on it. For it to be stuck on “rifle” it has to have been stocked AND barreled.
No idea on the date of the letter I posted, as I can't find the first page that goes with it.
Here's a 2010 letter which mentions "barreled" only, not "stocked and/or barreled" and would seem to supplant the 2004 letter...
IIRC, there's another letter floating around, and I can't find it at the moment, stating that a completed lower (even with stock) may be built into a pistol since it's never been barreled as a rifle.
If you don't want to use a heavy barreled upper, I suppose this is an option. But since you can have pretty much any barrel length at that point, I'm not sure why you'd go with 16".
Did you zero the red dot? Just because the dot is showing up in the middle of your front sight doesn't mean it's all going wrong.
What people are generally talking about when they say "co-witness" is having your optic and sights set up in such a way that either/both can be used without...
Just remember that the FBI is moving back to 9mm :P
And more than likely nothing will come of the Army looking into moving to another cartridge.
Regardless, with modern defensive ammo, you should be good to go with whatever caliber you choose.
The "Other" is not on the 77r (although that category is on that form), it's on the Federal 4473 you fill out.
https://www.atf.gov/files/forms/download/atf-f-4473-1.pdf
pg. 2 of 6, section B, number 18.
You'd be better off asking them directly, they don't bite. I know their prices vary based on the features.
Someone on the sight may be able to help you put it together.
If you buy all the parts, it could be that Engage could put it together for you, but again, ask them directly.
Do you need it to be an HBAR upper?
If yes, go visit Engage Armament in Rockville and see what they have in stock / what they can put together for you.
If no, then I'd recommend BCM, especially with their current sale that includes the BCG. It'll be more expensive, but it will work and...