What muzzle brake or flash hider is on the gun? Some of them I nickname "Loudeners". Some like the AK74 style brake are just flat out painful to shoot from a hearing standpoint.
This is my Kel-Tec PLR-16 .223 with a 9" barrel. It is PAINFULLY loud without proper hearing protection, and by that I mean both squishy plugs AND ear muffs. Muzzle flash for most ammo is about the size of a watermelon. It's just not a pleasant gun to fire, yet recoil is like a .357 Magnum in a S&W Model 27.
(And yes, it is tax stamped as an AOW so the vertical fore grip is legal.)