If I recall correctly, at one time owning one without a stamp was a no-no. Like a few other M-16 parts, a felony just to posses them?

Now, they seem to be in regular use. Always preferred for certain applications & seems to be used a lot now. Guess I missed the memo, ATF change this alone? other parts? or was the carrier mistaken to be a no-no all along.?

Mainly curious, but always trying to be on safe side.