Looks for one. Rigidity for another, especially if you're using open sights.
Longer options. The 12.5" is what should have come on the rifle. Some people like having the front of the hand guard right up to the flash hider.
Push button sockets with limited rotation.
The barrel IS free floating. The plastic hand guard end cap is useless decoration that just pops right out.
Hopefully there's not that kind of weight on a bipod.
There is only one manufacturer in the world that makes aluminum hand guards for the 15-22 that actually fit them perfectly.
You can get the adapter and do some machining yourself, but the time it would take is a bit and the final product...well...depends on how good you are or how much you...
The ejector has been addressed
The extractor is the other culprit. Get this to fix that issue - S&W M&P15-22 Extractor Set (3 Pieces) | Tacticool22
Another problem is if you have a "Bad-***" lever on the release paddle. Some of them are too heavy.
The firing pin is "supposed" to stop before it...