I was recently talking with a friend, with whom, we both share a mutual friend who ran the slot department for many years under Bill Harrah at Harrah's Reno and Harah's Tahoe. My friend relayed the following story:

During the 195's and early 1960's, Harrah's would purchase real U.S. silver dollars for use in their machines. They would get these silver dollars from the mint, in new, uncirculated form. The coin bags would frequently contain uncirculated silver dollars from the turn of the century up to the 1920's! When they would place the dollars into the machines, coin collectors would come in and buy many of these dollars leaving them short on coin for their slots. The solution that they came up with was to dump the coins into a cement mixer and tumble them until they were sufficiently used. This would emlinate the coins from walking out the door!