Psst ... Wanna Buy A Piece Of Christopher Dorner?

Now this is special ... Dead cop-killer Christopher Dorner's .38 Special is up for auction.

Dorner got a piddly fifty bucks for the well-worn revolver (pictured above) at Bargain Pawn in January, a month before his killing spree touched off one of the largest manhunts in LAPD history.

The North Las Vegas pawn shop started its online auction Tuesday evening ... so far it's up to $455 with 15 bids. A permit and photo of Dorner in the shop prove it was his.

The owners tell TMZ they have only good intentions -- the listing calls Dorner a "coward and murderer." They're donating the proceeds of the auction to the families of Riverside police officer Michael Crain and San Bernardino Det. Jeremiah MacKay ... who both left behind kids.