I have a chance to buy a DPMS reciever which I like very much, but I'm concerned about the cast recievers. I have heard about k-booms with the cast rec. and I'm not so crazy about that. Also the guy who is selling the reciever doesn't exactly know if the reciever is cast or forged, how can I tell by looking? is there a special serial number to watch out for on the cast ones. The recievers serial number is CXXXX with four digets. Does the C before the serial number indicate that its a cast reciever? Need help Identifing. thanks.

I believe that is a Cast lower.. the cast ones have a rougher surface.

See that little "c" shaped groove running up and down the front inside of the magwell? If the lower has it its most likely forged.

I believe all DPMS forged lowers have a F in front of the serial number... i know mine does.

DPMS cast receivers have not had any "KABOOMS" that I have ever heard of.  In fact, no lower has ever had a KABOOM.  AR KABOOMS usualy happen due to overpressure in the bolt/barrel extension area.  And it won't matter if the receiver is cast or forged, you will still pick it up in little pieces.  See "AR15 Kaboom" on the web for 3 very interesting stories. 26 tons of pressure doesn't differentiate between cast vs. forged.  

That being said, the lower of any AR is not a very stressed part.  The areas receiveing stress the most on a lower are the hammer and trigger pin holes.  There was a very good post  with pics here awhile back about a DPMS Cast lower which cracked when it was dropped.  Very interesting read.  

And why buy from some jag-off who has no idea what he is selling???  Buy yourself some piece of mind and get a new one that is forged.

I could be wrong but I believe all the markings on the cast lowers are embossed rather than being engraved.

Yep.. Most I have seen are raised not embossed.