This hypothetical question was spawned after a very literal situation I stumbled upon. Recently, a family friend of mine, successful businessman, father, long time firearm owner, and generally very intelligent man, posted pictures on Facebook of himself and his son committing what was very obvious to me, to be a felony (or multiple felonies). He had a Masterpiece arms 9mm pistol, this exact one: https://www.masterpiecearms.com/proddetail.php?prod=MPA30T . In said pictures, he had one picture with a forward grip screwed onto the barrel, and another picture with a stock attached to the rear of the gun, and one picture with both. While not the exact forward grip or stock seen in this picture, it looked somewhat similar to this: http://www.usmachinegun.com/prodimages/DSC01180.JPG . I commented on the picture with both installed, and simply asked, how had he managed to get a tax stamp for a SBR? He responded saying it wasn't an SBR. I responded with some wikipedia links and a link to this site, and explained that he had in fact created a SBR WITHOUT a NFA tax stamp (as you cannot even obtain them in our state, sad face), and that he should remove the pictures from facebook. He did, and thanked me for the correction, and stated that he simply did not know of the laws defining what a SBR or AOW is. My hypothetical question that spawned from it, is regarding AOW's, and specifically the creation of an AOW when you install a forward grip on a pistol. From my understanding, if you put a forward grip on a "pistol", whether its the Masterpiece Arms pistol linked above, or a Glock 19, and do NOT add a stock, this makes it an AOW, and NOT an SBR, correct? Secondly, AOW's ARE legal in WA state, correct? The only AOW's that I am personally familiar with are the Serbu Shorty type weapons, and my understanding of those is that they require a $5 tax stamp to purchase, or "transfer" one to yourself. Now, my question is, is that same $5 tax stamp used if you wanted to create an AOW by putting a forward grip on a pistol? I found a small excerpt on Wikipedia saying that a "AOW Transfer Tax Stamp" is different than a "AOW Manufacture Tax Stamp", is that really the case? And secondly, would said "pistol" forever be an AOW, even if you remove the forward grip? I ask this, because if you were to hypothetically create an AOW by putting a forward grip on a Glock 19, and then remove said forward grip, could that Glock ever be carried concealed again, with a CPL, since it is now registered as an "AOW", and is no longer a "pistol"? I know this is a pretty wordy, and rather technical legal question, but I hope someone with more precise legal knowledge can answer it for me. thanks guys Edit: If this belongs in the NFA section rather than this section, my apologies.