Pistols? He hadn't really been serious about swords, was Macnair mentioning pistols in the same way he'd mentioned swords or did he genuinely want to use pistols? Was he only competent with healing spells? He'd much rather duel with magic but he didn't want to look like a coward, nor give Macnair added confidence if they did end up using pistols in the end. "If you want to settle this like a muggle then so be it. I'd rather not watch you struggle for a non-healing spell mid-duel, it would diminish the victory somewhat." He was no relishing the prospect of practicing his shooting but if Macnair was serious then he must be more confident with a gun than a wand and he couldn't afford to leave it all to luck.
