1a count for installments/stages (as in 第〜弾) — used to number parts of a series, releases, or campaigns.
映画の第2弾が来年公開される予定だ。
The second installment of the movie is scheduled to be released next year.
キャンペーン第3弾として新商品を発売する。
We will launch a new product as the third phase of the campaign.
その企画は第1弾で好評だったため、第2弾が企画された。
Because the first installment of that project was well received, a second was planned.
2a count for bullets (used in contexts referring to ammunition or bullets).
地面に小さな弾が落ちていた。
Small bullets were lying on the ground.
マガジンには弾が十発入る。
The magazine holds ten rounds.