Thanks everybody for your input. You've answered my question and it's obvious that a suppressor is the only way to effectively cut the sound level down. I'm only going to be shooting indoors during load testing so I'll offer the other shooters earplugs and not worry too much about it. I've been in there plenty of times when other guys are shooting their 16" barreled AR10s and they don't seem too concerned about other shooters. It's a gun range and gun ranges are loud.

Nic, thanks for the tip about QD vs direct connect suppressors. I'll definitely keep that in mind.