I've heard of them, but what exactly is it.  Anybody got a photo of what one looks like?

Also called a recessed crown.  Helps to protect the muzzle.

So it's just a recrowned muzzle then?  Heck, I've done a couple of those myself.

Well I have a few in my collection. What is really is, is when you drill out the bore from the muzzle end of a barrel. It is used to restore the accuracy of a barrel that has muzzle damage. If you counterbore the barrel an inch or so you get back to the good rifling and it can bring new life to a bad barrel. It is common to see it done on old Mausers or Mosins.

Sorry i don't have any pics but they don't look anything like the ones posted here so far. I think those pics are of target crowns more then counterbored muzzles.

... technically, it's not drilled, it is counterbored.

... and, it's advisable not to use a pilot when machining the crown - nothing other than coolant should touch the bore during the operation.

Quoted: Sorry i don't have any pics but they don't look anything like the ones posted here so far. I think those pics are of target crowns more then counterbored muzzles.

That's what I was thinking the pic was.  My M24 has the recessed crown, and looks like the pic that was posted by Slaughter.  If counterboring is a repair step, then that is definately not what I was thinking of.