Thinking about buying a M85 NP today after work. I have to commit to the seller pretty quickly to arrange meeting this afternoon and dont have much time to read into threads on this particular gun.

Do these take brass ammo good?  Part of the draw to this particular gun is being able to use my AR mags and ammo with it, which will only be brass.

Does it shoot both .223 and 5.56?

How is the overall reliability on these? I read something quickly that newer ones have issues that older ones do not? (IE bolt sticking, FTF)

Is $500 for an unfired safe queen with (1) 30rd mag a decent buy?

Takes all kinds of 223/556 ammo just fine. Steel to match. Yes it's a 5.56 pressure chrome-lined barrel as per NATO specs.

I've never had any issues with the M85 so i can't comment on anything besides the one I've used - but it was 100% flawless.

IMO $500 is high. They are around $450 new with two tapco magazines which are worth about $1 each.

My 85np is 100% reliable. I trust it more than my AR. It ate both steel & brass without issue. I only shot .223 cal.
BTW, my 85np came with 2 magpul m3 mag. I paid 479 for it. 

Do it
Mine is awesome
I've got an approved stamp but haven't put a stock on it yet

I just ordered an m85np from sportsmansguide less than an hour ago for $486 shipped. supposedly it comes with two pmags as well.

Yep, with the free 30 day trial membership............this is the route I decided to take as well, bout to order here in a few minutes