円弾 is read as えんだん (endan) and means round shot.
えんだん
endan
えんかつ
smooth
えんばん
disc media (CD, DVD, etc.)
えんじゅく
ripeness
えんたく
round table
えんこ
arc
えんかん
circle
えんばんなげ
discus throw
えんじん
circular (battle) formation
まるやまは
Maruyama school of Japanese painting (Edo−Meiji period)
えんか
value of the yen
まるてんじょう
arched ceiling
えんかんたい
solid torus