I found a Colt "Sporter Lightweight cal 9mm Nato" with serial #NL00103x.  I think it's preban, it has the birdcage flashhider, but NO bayonette lug.  How do I find out?  What's its worth?  Like new?  Comes with 4 Colt mags, 2-20, 2-32?'s  Thanks for your time.
Jordan

Try this for a quick serial number check --> www.biggerhammer.net/ar15/ar15serial.html  

Indication is that this is pre-ban.

To be safe, always call the manuafacturer if possible.  

From your description, it is a blue label rifle, which means no bayo lug, sear-blocked lower.  The mags are probably worth $80 - $100 a piece by themselves.  I frequently see blue label rifles around $1400 - 1700, though usually not with so many Colt mags.  Green label rifles I've seen for $1600 - $2000.

I have one of these, and they are fun and accurate, especially with zippier rounds.  It is also a plus if your indoor range does not allow rifle calibers because ranges will usually let you shoot pistol caliber rifles.

Hope this helps.  

Turborocket,
    Thanks so much for your inputs.  That was more info than I've learned with about two hours of research.  Thanks.  If anyone has anything to add, please do.
Thanks,  
Jordan

mags sell from $100 to $140 range, if you buy it be sure to get all the mags,
<mags suck to load!>
I have colt 9mm car and love it,

Thanks K-9, keep the input coming guys.  He is looking to trade for an SP1 with forward assist like new and a few mags.  What do you guys think?

find out what he wants cash, that gives you a better idea what kind of deal he's trying to make.
the colt 6450 with a "TA" serial # green label are selling for more, there not marked sporter there marked carbine.

That was a good idea to find out the cash value he puts on it.  I have a brand new in wrapper and box I paid $1,089 for which came with two 20 rounders.  One year later I paid $180 for three new in wrapper 32 rounders.  Of course, it has been nine years or so.  I still have them new in wrapper and love fondling them.  Good luck with your purchase. Sounds like you are getting a good deal.
ralph

btt    still trying to decide, so is he

Quoted: Thanks K-9, keep the input coming guys.  He is looking to trade for an SP1 with forward assist like new and a few mags.  What do you guys think?

Make sure the magazines are COLT, and nothing else. Make sure they hold the bolt open when empty. Modified UZI magazines suck and do not hold the bolt open.