Two layers: literally 'bird-gun' = a small-bore gun for shooting birds; in late Qing texts
鸟枪 also refers to the matchlock/flintlock muskets adopted from European traders. The set phrase
鸟枪换炮 (niǎoqiāng huàn pào) 'swap the bird-gun for a cannon' = a major upgrade in equipment, status, or scale.