Not sure if this is the right place for this but maybe someone has done something similar here.

I am planning on building my first sbr in 300 BO for my Rugged Obsidian 45(still in jail pending 7/21/16) to go with it. I wanted to know if going with this set up would be ok or a bad idea. The hand guard is an Aero Precision AR15 Quantum KeyMod Handguard - 9" with a diameter of 1.78" which would have enough clearance for the Obsidian. Assuming I use direct thread to attach the suppressor, would I have any problems?

Thanks

Should be no issue with it under the rail, but I would use a 3 lug adapter.

Would the 3 lug adapter be stuck on the barrel then like if I wanted to change it I'd have to take off the handguard?

No, it's held on just by spring tension, it's pretty much twist off.