Yes. The BATFE recently published a ruling which clarifies this – here is the link:
https://www.atf.gov/file/55526/download
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There has been a lot of misinformation circulating to the effect that once the pistol lower has been assembled to a rifle configuration then converting back to the pistol constitutes ‘making a pistol from a rifle’ and thereby placing the pistol into the SBR (short barreled rifle) class. Not so.
Please see our Forum for even further clarification. It is the first post on the Forum so you don’t have to spend time trying to find it.