I know this is a really unorthodox idea and might be really stupid, but give the idea a chance. I have seen some 10/22 barrels with a "shroud" built into them to make the 16" leangth. The Tactical Solutions SBX comes to mind. Then the supressor drops into the shroud to give a short overall lenght with can in place. It crossed my mind that you could do almost the same with an AR15 using the hand guard.

The why to all this is kind of simple. I have a few SBRs but they are difficult  to travel with and I travel interstate constantly. I want to hunt with the rifle and some states dont allow hunting with a pistol and a brace. So no SBR and no pistol.

So this was my thought. A perminantly attached supressor would work but has drawbacks. So I started thinking, 12.5" 6.5 Grendel barrel. Direct thread TB Ultra 5 or 7. Then used something like a 17" Odin works rail or BCM KMR if they make one long enough.

Depending on the design of the rail a small spot weld on any of the screw heads would make it perminantly attached. Something lile the KMR you could put a spot weld on the end on one of the screw to the head of the other screw. If you needed to grind it off simply replace the screws. Something like the odin works would need a small steel "bridge" between two of the screw heads with a spot weld on each. You could do this on the bottom two where it is less visible.  

Since the barrel would be shorter than the hand guard this would obviously be run supressed 100% of the time. But the can could be removed for cleaning and servicing unlike a perminantly attached supressor.

I know this sounds really strange but would the idea satisfy the ATF the way a the Tactical Solutuons 10/22 SBX barrel does?

I think the law specifically says the barrel must be 16".  If a flash hider is not pinned and welded. Maybe I am not understanding your idea properly.

It would work, but the rail/handguard would have to be permanently welded to the actual barrel, not just the barrel nut or the upper.  Only "barrel shrouds" permanently attached to the barrel itself count toward it's length.

Ok, I guess that answers it. Not really worth going that deep down the rabbit hole.

I understand where you’re going with your idea but with the suppressor not permanently attached the ATF will still say you have a 12.5” barrel! In my opinion.

If you find a decent machinist, they could do the same thing Tac Sol does.

Dennis Brush, before he passed, made the "Really Big Flash Hider". It was just like the tac sol, but sized for rifle cans. You just need someone that can recreate it and that would solve the issue.

Sounds like you would need a shroud that can be welded to the barrel, leaving the threads for the suppressor. OD small enough to fit inside of the handguard and ID big enough for the suppressor to fit into. Could also serve well as a heat shield. This would be an interesting project.