I'm considering buying a colt m16. Anything to specifically look for when I go to check it out? It's listed at $23,900.

The first thing that comes to mind right away is look for egged (i.e., deformed) hammer pin holes in the lower.  That would be an immediate deal breaker for me.  Finish on the lower should not have any wear, scrapes or scratches at that price for an A1.  Make sure all the parts - stock, pistol grip, internals, entire upper - are original and in a condition commensurate with the price as well.

MHO, YMMV, etc.

Good luck!

I wish I could get the one I used In basic ...  # 4159158    I'd give 25K for it

Transferable M16 machine guns and estimated market values:
RLL $13-15k
RR AR15 Auto Conversion $16-19k
RR Colt M16 & M16A1 $21-26k
RDIAS $22-28k
RR Colt M16A2 $28-33k

Websites to watch for good deals on machine guns:
http://www.sturmgewehr.com
http://www.shootersdepot.com
http://www.atfmachinegun.com
http://www.autoweapons.com
http://www.impactguns.com
http://www.subguns.com
http://www.onlythebestfirearms.com
http://www.davidspiwak.com
http://dealernfa.com
http://www.gunbroker.com
http://www.nfasales.com
http://www.classiiidealers.com/
http://www.westernfirearms.com/
http://www.urban-armory.com/

Website that tracks machine gun values:
http://www.machinegunpriceguide.com/

As for what to look for...remember when buying a colt M16A1 you are paying $5-10k premium for the "history" and/or collect-ability of the Colt name. If you want a shooter to use and abuse i would go with a conversion rifle like a Colt AR15 slab side or a non-colt Olympic Arms, but if you plan to take good care of it then look for a colt M16 that has not been refinished, repaired or has excessive wear of the anodizing or pin holes.

Feel free to post up pics here for some feed back. Assuming its roll marked Colt M16 or M16A1 i would say $23,900 is a Fair deal, not a steal but not getting ripped off either.

Just some general advice, if you buy online out of state or a personal transaction in state, IE not from a in state dealer you can avoid sales tax, which can easily be $1,500 on a purchase of that size.

"Just some general advice, if you buy online out of state or a personal transaction in state, IE not from a in state dealer you can avoid sales tax, which can easily be $1,500 on a purchase of that size."  Not entirely correct in Michigan.  Online out of state purchases over $1000 must be reported, and the sales (aka use) tax must be paid.  See, for example, a 2014 Michigan Income Tax form, or look it up on line.  Your state laws may vary.

Fair enough, depends on the state your reside in I guess, but still something to consider.

Its at a dealer and they will let it go for $23250. Comes with two colt uppers, one is a heavy barrel. Internals looked to be good shape and receiver is in nice condition other than one scratch. Sorry didn't  get any pics but going back to look one more time.

Look closely at the trigger guard ears, threaded areas, and take down pin areas for cracks.

Bring your own upper to check fit. Check the F4 for registration by Colt.

Look in the interior for any sign of welding.

If the finish is perfect it is probably/may be refinished.

Look at photos of mil-spec M16s and compare to the gun.  Anything other than roll engraving is suspect.

Spots of black paint at recoil tube lock ring staking and bolt release roll pin are a good thing to see. Absence is not bad, may have been cleaned off.

did prices come down?   I see A2 guns selling for $27-28k.      Back when A1s where just north of $15k, A2s were $25k.

No, $27-28 is just the low end of the value range. All depends if it's a private sale or a dealer, how desperate the seller is, condition of the rifle, other MGs on the market at the time, etc...prices will always fluctuate a little bit but unless something changes legally about MG ownership prices will never go down long term, only up.

a seller with a huge pile of mint A2s dumped them on the market recently and created a mini-recession

the tidal wave of A2s will all disappear again into private collections and you'll see the prices go back up

Well buy while you can at these prices i guess.