O.K., I know I can't put an 11" pistol upper on a rifle lower, but how about a 14.5" upper? Do I still need a "new" lower for that build? I did some hunting here and found this in a sticky: So as an average consumer you must keep in mind that your total barrel length must be at least 16” inches long. The total length of your barrel and muzzle device (flash hider (FH), muzzle brake, or compensator) is used. You may purchase a 13.7” barrel and have a very long muzzle device (such as a Noveske KX3) pinned and welded to it to get it to the 16” overall length. Or you may opt for a 14.5” barrel, with a muzzle device, pinned and welded to it, to bring overall length to 16” So it appears that I need to confirm the overall is 16" correct? After more checking, I guess it needs to be pinned or welded.