My S&W M&P Sport II was my first AR15. I have since acquired a couple more ARs that are other makes. Compared to the others, I've noticed the bolt catch in the S&W lower receiver seems rather loose with a good bit of play front to back. You can slide the bolt catch lever sideways back and forth in the receiver slot maybe .025" and see the gap on either side. The bolt catch slot measures about .175" or so, as do my other lowers. The bolt catch thickness in the S&W measures about .145"; the bolt catch in my other ARs is thicker and measures about .155" (at least .010 difference). 

I don't mean to be a perfectionist, but this is a noticeable difference. With the bolt catch engaged and holding the bolt back, the lever button is not completely vertical and angled toward the front several degrees crooked. 

Is this right? It seems to me I need either a thicker bolt-catch or small steel shim washers on either side of the bolt catch. You can already see a small indention on the bottom right of the bolt catch slot where the BC is hitting the inside of the slot when holding the bolt back on the last round. It seems to me the excess looseness is causing excessive wear in this area. 

Any ideas or opinions appreciated. (I also posted this in the S&W Industry forum, but it doesn't seem to have much activity lately.)

Thanks   

Just buy a new bolt catch if it bothers you. Many options to choose from and it won't break the bank. Not hard to swap out and it'll be one less irritant for you to be concerned about.

Alternatively, you can just send the gun to me so you wont have to be bothered by the floppy bolt catch ever again...

Thanks for the replies. I appreciate it.

Like I said, I don't mean to be a perfectionist, but the bolt catch on my other ARs are good and snug, but still plenty of room to function smoothly under most any condition. They probably have that .010 play Dano mentioned. 

I have built a few stripped lowers and have the special BC roll-pin punch from Brownell's, so I'll decide if I want to try another catch or go with the shim washers. Not sure it's worth sending back to S&W when I can do something about it myself.

Thanks! 

I also posted this over on the Industry S&W sub-forum here. The S&W rep ask for pics. I thought I'd add the pics here too, so you guys don't think I'm making this up. Not that you'd think that anyway. 

The pic on top is the bolt catch lever button in the static position, not holding the bolt back (no pressure on bolt catch). The pic on the bottom is with the bolt catch lever holding the bolt back, pushing against the lever. You can see the difference in the position of the bolt catch lever release button. 

Update:

I have not heard back from the S&W rep here about the photos I posted on my very loose and sloppy fitting bolt catch on my M&P sport II. Of course, it really doesn't matter now, because I removed the bolt catch and put a .015 steel shim washer on the right side, and now the bolt catch is not as loose fitting, but still plenty of movement to allow for proper function. My guess is that it was either a slightly out-of-spec (narrow) bolt catch or a slightly out-of-spec (wide) slot in the lower, or a combination of the two. Either way, I'm happier with it now. 

So, I used an accu-shim (not accu-wedge) to tighten up the looseness between the upper and lower, and the .015 shim washer to tighten up the bolt catch. Turned out to be one of my favorite ARs so far.     

Sometimes I wonder how such a wide variation/tolerance of "mill-spec" developed over the years. I'm actually used to a little more precision, I guess.  

Oh, by-the-way, that special AR bolt catch roll-pin punch sold by Brownell's works great!!! No nicks, scratches or scaring.