noun
duplex; double-barreled; two-shot
Describes a mechanism or device with two linked barrels, chambers, or units, such as a double-barreled shotgun or a two-shot flare gun.
彼は二連式の散弾銃でクレー射撃を楽しんでいる。
He enjoys clay shooting with a double-barreled shotgun.
この信号拳銃は二連式で、二発続け
This flare gun is a two-shot model, capable of firing two rounds in succession.
連発式 means repeating or multi-shot, often implying a magazine or cylinder, whereas 二連式 is limited to two shots or barrels.
Compound of 二 (two), 連 (link, connect), and 式 (style, type). The term is transparently derived from its components.