Although they are not being consistent about the matter, the main issue is whether or not a pistol brace is a butt stock. First the ATF said it was not and people bought 40 million of them. Now they want to say they are, but their rules are ambiguous and confusing. Rather than just say they are a stock, they are saying you not only have to remove them (because a stock on a pistol makes it a SBR) they are saying you have to modify them so they can't be used. This makes no sense if they are a stock as they simply snap onto any tube on any AR15 regardless of barrel length, so why do I have to modify them? If they are just a stock, then I'm just not allowed to put them on a pistol. But I should be able to put them on any gun with a 16" or longer barrel. I wish they would at least clarify this. They tried this argument about owning a stock that COULD be put on a pistol when Thompson Center Arms came out with Contender barrels and stocks that could be used as a rifle. They arrested a man for owning both pistol stocks and rifle stocks and both short barrels (<16") and long barrels (>16") because they said he COULD assemble them as a short barreled rifle by putting the rifle stock on and a short barrel on. The judge said they could not charge him unless he actually assembled it as a short barreled rifle. Yet now the ATF is saying if you have a pistol brace, which they are now calling a stock, and a short barreled AR15 pistol that you own an SBR even though you haven't assembled it in that way. Which violates the precedent. I'm sure the courts will eventually sort it out, but I would not want to be the test case. The ATF has already been decided against in the bump stock rule and likely will get struck down or at least limited in this. The NFA SBR laws never made sense and has been changed several times because they don't make sense. At first all rifles had to have barrels 18" or more. Then they changed it so .22 rimfire barrels could be 16". Then when a lot of surplus 6.5 Swedish carbines and .30 M1 carbines came on the market with 17" and 16" barrels they changed it for high powered rifles. Part of the dilemma was that they had already sold thousands of the .30 M1 carbines to civilians and realized that they had made them all felons by selling them SBRs. The entire precept of all of the NFA rules was to outlaw "scary" rifles and shotguns (the ones being used by Gangsters that were not being used by civilians). Actually a lot of them were because the original law before being amended, was an attempt to outlaw pistols and so they were trying to outlaw any work around. Then they realized they could never get it passed with so they took out the pistol ban. It's not like a SBR is deadlier than a pistol. You can buy a pistol in any rifle caliber you like and it's not an SBR yet it's illegal to convert a rifle to a pistol even though that same pistol is on the market already. In other words, two identical guns and one is legal and the other is not.