What is Korean archery, Guk Gung??

I know I should have explained it from the beginning.  
Here is a few history facts from Wikipedia.

 The reflex bow had been the most important weapon in Korean wars with Chinese dynasties and nomadic peoples, recorded from the 1st century BCE.^[2] Legend says the first king and founder of the Goguryeo, Go Jumong, was a master of archery, able to catch 5 flies with one arrow. Park Hyeokgeose, the first king of the Silla, was also said to be a skilled archer. Rumors of archers in Goguryeo and Silla presumably reached China; the ancient Chinese gave the people of the north east, Siberia, Manchuria and the Korean Peninsula, the name of Dongyi (東夷), the latter character (夷) being a combination of the two characters for "large" (大) and "bow" (弓).^[3]
However, the word 夷 was first used in Chinese history referring to the people South of Yellow River over 5,000 years ago. Later, when Yi 夷 people joined the tribes of Hua Xia [華夏] Chinese, 夷 meant outsiders. By that time, DongYi refers to Korean, as in Outsiders from the East.

 Wall print of Goruryo (37~668)

You can find more information about Korean archery online.

Korean people were used horn bows for hunting and wars, well they still use them today, but as a sport.

The traditional Korean bow is a highly reflexed version of the classic Eurasian composite bow. The core is bamboo with sinew backed to prevent the bow breaking and to add a pulling strength to the limbs, with oak at the handle. On the belly is water buffalo horn which significantly increases the power by pushing the limbs. This combination of horn which pushes from the belly and sinew that pulls from the back is the defining strength of the bow. The siyahs, the stiffened outer ends of the limbs, are made of either mulberry or black locust spliced (v-splice) onto the bamboo. The glue is made from isinglass. Over the sinew backing is a special birch bark that is imported from Northeast China. It is soaked in sea water (possibly for one year). It is applied to the back using diluted rubber cement (using benzene as the solvent). No sights or other modern attachments are used.
The draw weights vary, but most are above twenty kilograms. The cost for this type of bow is in the US$800 range. For a similar modern version made of laminated fiberglass, the cost is US$200–300. For most competitions, either bow may be used, with carbon-fiber arrows, but for national competitions, only the composite bow and bamboo arrows may be used. Korean archers have also been very successful in Olympic and other competitions with more modern types of bow.^[5]
The sukgung, a kind of crossbow, and the Gak-gung are a small but very powerful bow. A sukgung can shoot up to 400 meters while a Gak-gung can shoot up to 350 meters.

Since Korean archery became sports, people often practice it on target that is 145 meter away.  The draw is longer than other styles, like Turkish, Chinese, western, etc.

All the images that are not mine are from google search.