S&W M&P15FT - Rail Questions

AR/M4 AR Technical Discussion
1

First off, hello to everybody, this is my first post.

Second, just got my hands on an M&P15FT, NIB. Once I got it home and really looked it over, I noticed that the quad rail was just a hair twisted and the clamping screws were not evenly tightened down. One side was touching and the other side had a noticeable gap. I got out my allen wrenches and evened them out and got the rail square to the upper. Now both sides are touching and it’s square. But now I’ve found that the rail is taking a slight dip down. If I put a metal straightedge on the upper and out over the rail, at the front site it’s dipping just a bit less than 1/32". I’m new to accessorized AR’s and don’t know if this OK or not. How precise are these set-ups? Also, beings as the barrel has no threads, what are your suggestions for a slip-on muzzle brake?

2

and found an instruction sheet on their MRF. From the looks of it, that’s what is on the M&P. They say to loosen it up a little and try again until it’s right. They even had a .pdf to download for reference. I was wrong in thinking that the only thing to watch for was twisting. Like I said, I’m new to AR’s with add-ons. I wish S&W had included Troy paperwork with the rifle. Also, still looking for ideas on a slip-on muzzle brake. I believe it measures at .750" and some slip-ons I’ve seen are .708". Who’s got options for me? I do have access to a lathe but don’t know much about the best materials to make one from scratch.