I took advantage of the free registration and received my approval in 30 days. It wasn’t like I didn’t already have several Class 3 items registered. One more won’t make any difference. The rule clearly states in their FAQ that once registered as a SBR, you can put any stock you want on it. I replaced my brace with a Magpul collapsible AR type stock. Since I have a few other AR15 firearms, does the possession of the brace become illegal on May 31? I’ll bet I couldn’t find an ATF agent that could answer the question.