Ancient Chinese Knife Money, What Is This Worth?

These are tricky. That is a nice tao. What's the weight? The shoulders and point are in XF shape.

n8b- Very interesting! As it has been said, these can be very tricky, and not just apropos grading. One must remember that in China counterfeiters have been making reproductions of their own coinage for a long time now, and that many soldiers returned from WWII with souvenirs that they bought in Asia. This caused a lot of well-made & convincing fakes to enter the US. Also, you should remember that ebay has introduced a lot of reproductions to the US as well. Finally, it is possible that it is real since some real examples have made their way to the US over the years, be they war souvenirs or other circumstances. Most museums treat these as the centerpiece of their Chinese coin collections, so that tells you that these are highly-sought after and not that common.

If the knife money is genuine it could be worth 450-650, it looks good

I also suspect it is a reproduction; while the zeno.ru database is not by any measure complete, the only match for your characters and reverse pattern I can find there is for some modern reproductions, like this one and this one.

The only "six-character" knives listed in the book by Wang Yu-ch'uan (published 1951) date from the early period of the State of Qi; the inscription on your coin seems to match the one in the book - the six characters translate to "Qi establishment state eternal legal knife-coin" - but the characters on genuine knives are much more archaic. Here's the plate from Wang:



On these Qi knife-coins, the top character, qi, looks like three stealth bombers flying in formation. On later three-character knives, qi looks like this, as you can see on this zeno example. But on your knife, the top radical has been truncated, as if the copyist ran out of room.

50 grams sounds the correct weight, but at six inches, it sounds slightly small; the one in the book is over seven inches, as is the zeno one I linked to above.