Living at my parents during the summer when I was in university gave me a chance to shoot in the country. We had neighbours across the creek, maybe 300 yards away, an older couple that we never saw. So I thought I would work up some loads for my Mini-14 one fine June morning. Using my picnic table as a shooting bench I put a target 100 yards out (we had a big lawn!). After about ten rounds I could hear the faint mufled sound of somebody yelling. After taking out my plugs, I could hear the old lady swearing about all the noise! It was priceless. I shut it down pretty quick after that. I thought the noise wouldn't be so bad, but I was wrong.
My next range became an old gravel pit about 2km from my house. My parents would comment that they could hear the shots when I was there. So, there's my first hand experiences with my .223. I also recall a huge difference when I put on a muzzle flash suppressor, much more bark than a standard muzzle, but sure cut down the muzzle flash.
I still have a good laugh listening to the old lady in my head.....mother *^#^*$! Shut the &#(@$ up!