[Costa]

Most of the stuff I "know" about the M4 is related to what I've read about ballistics and tests comparing the M4 to the HK416 and others in an attempt to replace it.
I have no real experience with any AR series rifle to delve into practical questions... yet.

As for the comment earlier about the .223 round vs the 5.56x45 - The .223 is the civilian equivalent, BUT they are not the same as anyone who knows anything about anything will tell you. The 5.56 is a higher grain round which yields greater pressure. Due to this, the leade and case thickness of the two rounds differ. What does this mean to Joe? The bullet/barrel match is critical in achieving accuracy, range, and lifespan/reliability. Use the designated round for the designated barrel.

I 'think' the issued M4 has a twist rate of 1 in 7, however I could be wrong. I've heard 1 in 8.5 as well. I would however say I'm pretty sure that the twist rate is faster than 1 in 9 to allow better stabilization in higher grain rounds to achieve range and accuracy.

As for flaws? I know the main differences between the 416 and M4 are that the 416 is a Gas-Piston operated rifle as opposed to merely just gas. Yada yada yada... greater reliability all around from practical use to lifespan.

I know most guys that shoot professionally get trigger jobs and free float hand-guards installed, and I see a lot of charging handle products. This would lead me to believe that these areas need attention.

Please enlighten me.

Also as for "rail gear", I would imagine that whatever "gear" is needed to get the job done is used. No more, No less. Whatever the mission requires. If a piece of gear can be utilized and the cost/benefit is positive (in this case cost being weight and space), it probably gets used. If it's unnecessary, leave it at home.