Modern AR’s built from quality parts are fantastic weapons. Super accurate, dependable, and fun to shoot. There are a crazy amount of parts available and they are super easy to build. Brownell’s is a great source of parts, tools, and information. Purchase a good builder’s tech manual and hit me up when you are installing the barrel.
The .300 blk in subsonic is very quiet with the correct suppressor. Do yourself a favor and purchase some distinct magazines to use ONLY for the 300. If you accidentally cross the streams and get a 300 in your 556 gun you will blow it up. I have seen it too many times.
Do a SBR!