Korean Cast Coin

That looks like a Korean sangpyeongtongbo hojo dangiljeon, or a Sangpyeongtongbo 1-Mun (cash) coin cast at Hojo, or the Treasury Department.

Yes, a catalog does come in handy when collecting Korean cash as well as all other Asian cash coins.
For the Sangpyeongtongbo alone, there are more than 5000 varieties. And some of the varieties are very hard to tell apart, because it's the subtle difference of the size of the characters, the style of the characters, the type of the characters, etc.
At least a basic knowledge of traditonal Chinese characters will be needed to identify them.
Very subtle differences between types compared to Western coins.

Unfortunately, I only dabble in Korean cast coinage, and it's not the focus of my collecting so I do not own one.
However, I think Hartill catalog for Japanese cast coinage and Korean cast coinage is good based on what I hear on this site.

Yes I already seen it, but I didn't find the coin there, could you find it?

I have the Hartill books for China, Japan, and now Korea.

I am prejudiced as I do not have the older references, but I am happy with the Hartill books and do not plan on replacing them.

I have read online USA dealers like Scott Semans, Frank Robinson, and Bob Reis universally praise the books and say that the older books are made (almost) obsolete.

The other available references are old, out-of-print, and expensive. Old China references are Fischer-Ding or Schjoth, old Japan reference is Munro, and old Korea reference is Mandel. If you look for these on ebay they will be expensive, so I figure why bother when Hartill is up-to-date and more thorough?

Please note this relates to English-language references. If you can read the original languages you have many more options.

I also have an old JNDA (Japanese Numismatic Dealers Association) book which has English legends but Japanese text. Although I don't read Japanese I can understand most of the important things - mintage, rarity, value, etc. . .

-wheatiefan