It was like a gift from the AR Gods.

Amid much skepticism at last year’s Shooting, Hunting and Outdoor Trade Show, Sig Sauer promoted an invention that would within a short few months utterly transform a market that had remained on the fringes of the shooting public. With a seemingly minor ruling from the nation’s top firearms regulator to an obscure suburban Colorado police department, the new accessory proved the catalyst for an explosion in popularity of the AR-style pistol, giving once-reticent purchasers a new reason to consider the short-barreled oddity.

But within less than a year — and after hundreds of blog posts, YouTube videos and letters to the agency questioning its use (or misuse) — the ATF reversed itself, turning some would-be users into potential felons and throwing the entire AR pistol market into disarray.

This is the short and tortured story of the Sig Sauer SB-15 Pistol Stabilizing Brace, or “Sig Brace,” that at once launched a new industry in the AR market and called into question the Depression-era rules that govern firearms in a very different world.

Ugh, What’s That?

Quietly launched midway through 2013 by inventor Alex Bosco and his company SB-Tactical, the SB-15 Pistol Stabilizing Brace was intended to help disabled shooters operate an AR-style pistol one-handed. The flexible plastic cuff wraps around a shooter’s wrist or forearm and an integrated Velcro strap secures the brace in place.

The idea was hatched in 2012 when Bosco was shooting with a disabled friend who was asked by a range officer to stop shooting his AR-15 pistol because of poor control of the firearm.

When he returned home, Bosco started tinkering with soft foam and a plastic modeling kit to solve the stability problem, and the rudiments of the SB-15 brace were formed.

With a prototype in hand, Bosco said in an interview on his SB-Tactical website that he realized it would be prudent to check with the Bureau of Alcohol, Tobacco, Firearms and Explosives to make sure his invention wouldn’t run afoul of any laws.

“I didn’t know anything about SBRs, NFA items or anything like that … I didn’t understand the implications of it,” Bosco said in the interview. “But I knew the best thing to do was to write a letter to the ATF.”

In two weeks Bosco got his answer.

“They said as long as the intent of the device was to fire the weapon as it was defined — as a pistol with one hand — they were OK with it,” Bosco explained.

With the letter in hand, Bosco began his search to find a firearms manufacturer to help him build and distribute the brace. He found his partner in Sig Sauer, which makes a variety of high-tech modern firearms and likely saw a way to expand its reach into the pistol market with the SB-15 brace.

After back and forth between Sig’s compliance officer and the ATF and a ruling that the accessory was kosher for pistols, the SB-15 brace finally debuted under the Sig Sauer brand at the 2013 National Rifle Association show in Houston. Initial reaction from shooters was muted, with many proclaiming the brace an abomination — an ugly add-on that wasn’t quite a stock, wasn’t quite a grip for a pistol that only had a niche market.

Others, however, saw an opportunity.

Not A Stock?...

In the past, AR-style pistols claimed the hearts of only a small percentage of shooters. Though it fires a standard rifle round, the length and weight of the AR platform — and even AK variants for that matter — made shooting a pistol in that configuration a chore. Some builders installed buffer tube pads and others experimented with devices that offered a suitable way to offset the weight, but none really pushed the gun into the mainstream.

The tepid popularity of AR pistols stemmed mostly from the Byzantine firearms laws enacted in the Depression-era 1930s. At the time, Congress passed the National Firearms Act, which among other things required anyone owning a rifle with a barrel shorter than 16 inches to submit to a rigorous registration process and $200 tax.

Fast forward to the early 2000s. With the advent of the AR-15 platform and its wide range of accessories and configurations, shorter-barreled variants became more and more attractive to the everyday shooter.

But there was still that onerous NFA law that was written in the age of sawed off shotguns and Tommy Guns that precluded most from going short.

Enter the SB-15 brace.

“Aesthetically, if you looked at it from a profile, it looks like a stock,” Bosco has admitted. “The way it is designed and the way it is made allow it to be used as a stock. But it’s not a very efficient stock because it’s rubber, it’s malleable.”

Though it’s not “intended” to be used as a stock, many saw the SB-15 as an opportunity to circumvent the NFA requirements for a short-barreled rifle, slap a Sig Brace on their pistol and sling lead from the shoulder. While it’s not the best stock in the world, the Sig Brace seemed to make a pistol a heck of a lot more functional from the shoulder than other options out there.

As the 2014 SHOT Show rolled around, adoption of the brace on pistols was slow and skepticism of the functionality — and legality — of the Sig Brace remained, even among retailers who were reluctant to embrace the accessory for fear of running afoul of the NFA laws.

That all changed in March 2014 with the ATF’s response to a letter from Greenwood, Colorado, police department Sgt. Joe Bradley who wondered if shooting a Sig Brace-equipped pistol from the shoulder would reclassify the pistol into an SBR.

“Certain firearms accessories such as the Sig Stability Brace have not been classified by [ATF] as shoulder stocks and, therefore, using the brace improperly does not constitute a design change,” the ATF told Bradley. “Using such an accessory improperly would not change the classification of the weapon per Federal law.”

A New Market Is Formed

The shooting world exploded with the news. ATF had said plain as day that you could build, buy, or sell an SB-15-equipped pistol and use it any way you wanted — whether one-handed, from the hip or from the shoulder. Many saw this as a way to own either the equivalent of an SBR without the NFA paperwork, or use a brace-wearing pistol as a rifle until the SBR paperwork went through.

Blog posts were written, YouTube videos went up, and all of the sudden the AR pistol — and many other heavier pistol designs like short AKs and 9mm sub-gun equivalents — were all the rage. Industry responded with a surge in 10.5-inch, 7.5-inch and everything-in-between models that shooters could slap a Sig Brace on and let ‘er rip.

"You can skip the ATF wait, tax, and NFA paperwork and have what I would consider maybe 80 percent of the functionality of an SBR,” said one reviewer on a popular shooting forum. “It actually offers a pretty good cheek weld, if you don't mind how close in you have to tuck your carbine.”

Tim Harmsen, host of the 300,000 subscriber-strong Military Arms Channel on YouTube, posted a video shortly after the March ATF letter arguing shooters should feel free to shoulder the brace.

“It doesn’t come as a surprise to me that the ATF said it’s perfectly legal to shoulder the ‘not-a-stock’ device when attached to a pistol,” Harmsen said. “So, the proverbial cat is out of the bag and we’re now able to go forth and circumvent the asinine NFA laws with reckless abandon.”

“Until this news broke I purposely didn’t show it being fired from the shoulder in videos because I didn’t want to be ‘that guy’ that got the BATF to change their minds,” he added.

As the pistol market gathered steam last year, Sig publicly maintained that the SB-15 was intended to be used with one hand and not shouldered, but others say the company didn’t discourage shooters — or gun manufacturers — from misusing the device.

“I’ve been of the opinion that Sig knew exactly how we would wind up using the SB15 on our pistols but until now they’ve urged gun writers not to talk about it for fear of provoking the BATF into reversing their decision,” Harmsen wrote on his Bangswitch blog. “Now that someone outside of Sig has contacted the BATF and gotten a determination letter, they’re asking writers to share this information with the community as they see it as being beneficial. … And I agree, it is.”

Rumblings From Below

One of the things Harmsen and others warned was that the NFA regulations are clear about modifying firearms. Analysts and some in the legal community argued that as long as the Sig Brace was installed per the instructions and not tinkered with in any way, shooters were good to go. But make one small alteration, and you could be subject to NFA rules and risk prosecution.

Rather than risk running afoul of the ATF, several manufacturers and accessory makers started sending their own letters into the agency asking whether their brace-equipped firearm or SB-15 variation was legal. As gun writers and distributors started hearing about a wave of new pistols set to debut in 2015 that featured the Sig Brace, the first warnings of a shift in the ATF’s position rippled through the firearms community.

Early last fall, little-known shotgun maker Black Aces Tactical wrote a letter to the ATF’s Firearms Technology Branch asking if a Sig Brace-equipped shotgun they designed was subject to NFA rules. In its November 14 response, the ATF told the company its shotgun was good to go — with one caveat.

“The submitted weapon, as described and depicted above … is not a ‘firearm’ as defined by the NFA provided the SigTac SB15 pistol stabilizing brace is used as originally designed and not used as a shoulder stock,” wrote Acting Chief of the BATF’s Firearms Technology Branch Max Kingery. “However, should an individual utilize the SigTac SB15 pistol stabilizing brace on the submitted sample as a shoulder stock to fire the weapon from the shoulder, this firearm would then be classified as a ‘short-barreled shotgun.’ ”

In an interview, Black Aces owner Eric Lemoine said the ATF determination was about only his shotgun and had nothing to do with AR pistols.

“The only thing I can say is that the letter states that this applies specifically to this design only. … Just our shotgun,” Lemoine said. “If it’s an AR, it doesn’t mention it in that letter at all.”

READ: Could This Mean The End Of The Sig Brace?

Many in the firearms community agreed, arguing those who worried about the ATF changing its stance on shouldering the Sig Brace were misreading the letter and misunderstood NFA laws.

“The ATF letter … addresses an inquiry from Florida gunmaker Eric Lemoine about using a SIG Brace on a short-barreled shotgun. And only that proposal,” wrote The Truth About Guns’ Robert Farago. “It has nothing whatsoever to do with the SIG Brace and AR pistols.”

Nevertheless, others saw the letter as a clear indication that in the ATF’s eyes the misuse of an accessory could potentially change the classification of a firearm.

As the gun world was arguing over what ATF would do, another letter emerged — this time in response to an AR pistol maker — saying that if the builder’s intent was to make an SBR but use a Sig Brace as a shoulder stock and call it a pistol in order to circumvent NFA regulations, the builder could be subject to prosecution.

“If this device, un-modified or modified, is assembled to a pistol and used as a shoulder stock, the designing or redesigning or making or remaking of a weapon designed to be fired from the shoulder … this assembly would constitute the making of … an NFA firearm,” the ATF wrote.

Finally, as the nation’s top firearms manufacturers readied themselves for the largest gun show in the world — many of them set to debut brace-equipped pistols — the bottom dropped out.

Just days before the opening of the 2015 SHOT Show, the ATF released an “open letter” to the firearms industry and shooters reversing its March 2014 opinion on the misuse of the Sig Brace, saying shouldering the device constituted a “redesign” of a pistol into an SBR.

“The pistol stabilizing brace was neither ‘designed’ nor approved to be used as a shoulder stock, and therefore use as a shoulder stock constitutes a ‘redesign’ of the device because a possessor has changed the very function of the item,” the ATF wrote in its January 16 letter. “Any individual letters stating otherwise are contrary to the plain language of the NFA, misapply Federal law, and are hereby revoked.”

What Does This Mean For You?

Attorney Adam Kraut of the Prince Law Offices in Bechtelsville, Pennsylvania, specializes in firearms law and has been following the tortured history of the Sig Brace since it emerged on the market.

He was one of the first to see previous rulings as a shot across the shouldering bow and a warning to shooters who use the brace to skirt the law.

“It would seem to me that ATF was looking at all these people going and posting stuff on social media … and basically these people were using [the pistol] as a rifle, not how it was designed and intended,” Kraut said in an interview. “I think the argument that ATF is looking at is that it’s great that it’s technically an AR pistol as it sits there, but when you purchase that brace and assembled it, you either made it or remade it with the intention to be fired from the shoulder — that’s the definition of a rifle, and because the barrel length fits into the definition of a firearm under the NFA, here we are at illegal short-barreled rifle.”

READ: Law Blog Says ATF Hasn't Changed Ruling ... Yet

For its part, Sig Sauer released a statement reaffirming that the SB-15 was legal to purchase and use on a pistol as an arm brace.

“The Pistol Stabilizing Brace is legal to own, legal to purchase, and legal to install on a pistol,” Sig said in a January 21 statement. “Sig Sauer believes that the PSB improves the single-handed shooting performance of buffer tube equipped pistols, and offers the product both as an accessory and pre-installed on a number of pistols.”

Several sources who attended an ATF seminar at this year’s SHOT Show say agents with the bureau reassured manufacturers and retailers that the ruling was only intended to be applied as an extra charge in other felony cases. But legal experts warn retailers and shooters not to tempt fate.

Several prominent bloggers and YouTube hosts have since taken down their videos showing them shouldering the Sig Brace, including Harmsen’s Military Arms Channel. And while the firearms community is in an uproar, no one should be taking any chances, Kraut says.

“I would advise retailers if they have AR pistols equipped with any kind of brace … to ask their customers not to shoulder it in their store because this last determination letter opens the door to its becoming a short-barreled rifle, and that could potentially put them in some kind of position they don’t want to be in,” Kraut said, wondering if a customer shouldered a pistol in the store then handed it back to the retailer, does that make it an SBR and an illegal transfer?

“That’s still an open question,” he said.

In its statement, Sig hinted that it may issue a legal challenge to the ATF’s logic that by misusing an item a shooter has “redesigned it.” Some have likened this to using a can of creamed corn to hammer a nail. No matter what you do with it, it’s still a can of creamed corn.

“We question ATF’s reversal in position that the classification of the brace may be altered by its use,” Sig said. “We are reviewing the legal precedents and justification for this position, and will address our concerns with ATF in the near future.”

And while Kraut — who is also the general manager of King Shooters Supply in King of Prussia, Pennsylvania — is hopeful Sig will take up the challenge, there’s some doubt, since it’s unclear most people bought braces to actually use them as braces.

“My guess is that ATF looked at it from a broad perspective and said these people are really skirting the NFA [calling] it a pistol but using it as a rifle without going through the NFA process,” Kraut said. “While I don’t agree with the ATF’s position, I have a hard time believing that all of the [pistol] sales that occurred were from people who were looking to primarily use it in the manner for which it was designed.”