After the success of the SB-15 stabilizing brace, there has been something of an arms race (if you’ll pardon the pun) to see how far the ATF ruling can be pushed. Since the SB-15 is designed to be used as an arm brace and not a stock, adding one to your AR pistol doesn’t legally make the gun a “short barreled rifle” — and saves you $200 in tax stamps. A newer design is the “Shockwave Blade,” which is basically a single vertical rubber fin that hangs from the buffer tube of your AR pistol and claims to improve stability by limiting side-to-side motion while firing. The astute among you will notice that this device looks strikingly similar to a stock. So Shockwave Technologies asked the ATF to rule on whether it is indeed a stock. The reply was a bit surprising . . .

When the ATF issued their letter to SB-15 inventor Alex Bosco indicating that the SB-15 was good to go, they didn’t put any restrictions on that approval. He was free to use the device however he wanted. The intended purpose of the device was clear, and even if buyers used it raised it to their shoulders and used it as a stock, that was okay. The ATF has apparently realized the error of its ways and was a little less broad in its approval of the Shockwave Blade.

Based on our evaluation, the FTISB finds that the forearm brace, when attached to a pistol is a “firearm” subject to the GCA provisions; however, it is not a “firearm” as defined by the NFA provided the Blade AR Pistol Stabilizer is used as originally designed and NOT used as a shoulder stock.

Yes, they really did underline that section in the letter.

It looks like the ATF is keenly aware of how wide they threw the doors open when they approved the SB-15, and they are anxious to keep that from happening again. If I read this letter correctly, what the ATF is saying is that the Shockwave Blade is A-OK to install on an AR pistol, but if it’s used as a stock against the shooter’s shoulder, the gun becomes an unregistered NFA firearm. Basically, the item is OK, but the way the shooter uses it could turn a fun day at the range into a smorgasbord of felony charges.

This seems to signal that the ATF realizes it screwed up and wants to crack down on any copycats to Alex’s SB-15 design. They can’t rescind their original letter so they are stuck with that specific one, but for others trying to push the envelope, they will probably find a less than receptive tech branch at the ATF.