仗火 is dialectal/literary, mostly seen in older fiction and revolutionary-era writing. The standard modern word for combat is 战斗 (zhàndòu); 打仗 (dǎzhàng) is the everyday verb 'to fight a war'.
memory
仗 = 'battle' (as in 打仗 dǎzhàng 'to wage war'); 火 here doesn't mean literal 'fire' but is metonymy for gunfire / battle, the same 火 found in 火力 (huǒlì 'firepower') and 战火 (zhànhuǒ 'flames of war'). Together they reinforce 'battle'.
