Thanks to all here and the fantastic instructions, this lurker / newbie just built his first lower last night.  I took my time and was very careful, and everything came together and fit very nicely, with one exception.  My selector fits ok, and functions fine, but it just isn't as "crisp" as I would expect and has a little play in the "fire" position.  I haven't messed with AR's in years, but when I was issued a M16 in the Army I remember the selector having a very positive and crisp feel to it.  (It also had 3 positions... but that's a whole other thread....here
BTW, the lower is a DPMS, and I'm momentarily blanking on the part's kit manufacturer.

Thanks in advance!!

Mine is pretty crisp.

Don't remember any play.  It could be that the holes might be out of spec, but you could probably see that with your eyes.

You might check that the safety detent and spring are in there correctly.  

That is the only thing I can think of right now.

My selector felt a little weird when I first installed it, but I hit it with some CLP and worked it back and forth a bit.  Now it feels good.

I've noticed this with non-Colt parts kits.  I assembled a lower the other night with a JT parts kit, and the selector was very mushy.  I replaced the selector, detent, and spring with Colt parts, and it is smooth and crisp now.

Thanks for the suggestions!  I even took it apart again last night to make sure I had installed the detent and spring correctly, and it all looked correct to me.  I will make sure it is lubed well and see if it "works" in over time, and if not I may try a new selector (probably Colt....)  This would give me an excuse to add an ambi selector anyway!  Thanks again!

Quoted: Thanks for the suggestions!  I even took it apart again last night to make sure I had installed the detent and spring correctly, and it all looked correct to me.  I will make sure it is lubed well and see if it "works" in over time, and if not I may try a new selector (probably Colt....)  This would give me an excuse to add an ambi selector anyway!   Thanks again!

Except that Colt doesn't make an amnbi selector.  The DPMS ambi unit I have, however, works just fine.

Re the mushiness you hve experienced so far, you might have a grip with the hole for the selector spring drilled too deep, meaning that your detent pin isn't pressing the piece firmly enough to give you a crisp feel. Before spending any money, I'd pull the grip, and stick a small piece of cardboard (like a paper match chunk abour 1/8 inch long) down that hole, and try the selector again.  If it's still sloppy, you can always go the new parts route later.

It can just as often go the other way, the selector takes excessive force to move.

The detent is machined to a point, and sometimes this can be too sharp.  It will round off with use and become smoother, or you can speed up the process and hit the tip with a diamond file.

Sometimes there is too much tension from the spring, and trimming off a coil or two can help.

No matter whether the problem is too stiff or too mushy, you must be careful that when you put on the grip that you don't crimp or pinch the spring.  Do not slid the grip on haphazardly, but straight up.

are yousure you'vegot the right detent in there?

a friend accidentally put the bolt stop detend in the selector spot. it worked, but was very mushy and didn't lock very positively.

I'm positive I have the correct detent in place.  It is starting to work its way in a bit.  The selector has a much more positive feel than it did at first, although there is still a little play in the fire position.  (i.e. it wiggles about 5 degrees from vertical....)  I still may go for the ambi selector after watching my left-handed FIL struggle with the selector this morning.

By the way, my upper arrived thursday and took her out for the first time this morning.  First 100 rounds without a single hiccup.  What a hoot!!!  I had forgotten how much I love AR's.  It's been almost 10 years since the last time I fired the M-16 in the Army, and this was just like getting on a bicycle.

Thanks again to all here!!