You might want to read that new reg closely. The sighting system is now one of the criteria. If it has a rifle scope on it and you hold it touching your shoulder or face or chin, or ear, it looks like that is a rifle, certainly not a pistol because there is no traditional way where people hold a pistol and it touches your ear, nose, buck teeth, any facial hairs, chin, cheek, neck or shoulder. So, if it has a rifle scope and touches you above the waist when you sight it, if is a rifle and requires a 16 inch barrel.I did go and read the ATF Pistol Brace regulation and I'm good with what I have. The only thing I can't do is shoulder it. No problem, but you can tuck it into your cheek and the red dot lines up perfectly with your eyes.
I do expect a legal challenge on this new regulation and It would be great if they would reduce it down to two categories, either pistol or rifle and do away with the SBR category and the need for a $200 stamp.
The main thing is we need to do is to use the firearm in a safe manner, to me it doesn't matter how you hold it to be accurate.
The red dot and similar are not new, but the use on pistols has taken off the last decade, a red dot may be on a
crossbow, a pistol, a shotgun, a rifle, 😊 and red dots and lasers are now found on every sling shot, and certainly on the common arrow slinging slingshot (ASS.)
So now, if you have a red dot on an AR pistol, it does not mean that it is a rifle, unless some point of the gun actually touches you above the waist when you are normally firing it, but, it it touches, then the red dot makes it an SBR.
Everybody got it. You must read all 300 pages or so of the new rule to understand it.