The core challenge is demonstrating historical analogues for regulating specific firearm features from 1791 or 1868, as required by Bruen. Registration and taxation of firearms largely emerged in the early 20th century, making historical analogues difficult to establish for much of the NFA's framework.
However, lower courts remain split on these challenges, and the Supreme Court hasn't directly addressed NFA provisions post-Bruen. This area of law continues to evolve rapidly.
https://en.wikipedia.org/wiki/FPSRussia