It's necessary to clamp to the barrel to remove the flash hider.
Having made a 4.5 inch 15-22 SBR and knowing that clamping to the barrel is more difficult, I can tell you that you may need to improvise a barrel clamp tool that fits through the handguards to secure the barrel. It was easier with the old larger hole handguards. The new, thinner slotted handguards will require a narrower tool. I hope Tacticool could make and sell these tools.
I also had to improvise a barrel nut tool that had holes in it so I could clamp the barrel while the barrel nut tool while is tightening the nut.
I was wondering what S&W was using? If the barrel twists in the barrel clamp, the barrel will spin inside the receiver and the ejector will bend.
That may be why we're see so many extractor alignment problems in the other NEW 15-22 Pistol Announced thread.
Edit:
Here's how another member removed the flash hider back in 2016. It's a good visual resource. It's very good
except the part where he says to clamp on the handguards to tighten the barrel nut. Don't do that without clamping on to the barrel through holes in the barrel nut tool. It's kinda difficult so I'm sure that is why S&W made fine threads on the barrel nut.
http://smith-wessonforum.com/attachm...9&d=1487708410