I got my M4 early this year and only got around to breaking it in now over the easter weekend. Love the gun, it surprisingly didn't hiccup a single time even with light skeet rounds. But what I noticed it having dicked around with it before shooting it was that the factory clamshell forend was a completely solid fit with zero play UNTIL I put a few hundred rounds through the gun.
It seems like the break-in maybe heated the plastic enough to cause some change in form because now after taking it apart after shooting and putting it back together, I noticed there is noticeable play in the forend. By noticeable I mean that it creaks and moves about half a millimeter in the handguard retention plate with just a firm grip and there is a visible gap on the underside between the halves at both ends.
I'm curious to know if these generally have a little bit of play being plastic parts or are they supposed to be just an immobile fit. I found out that for some people the guns have shipped without the spring washer in the guide ring, but it is present in mine so that is not the problem.
