Correction, type 3 HMG, the rifle is type 38. Not a big deal, just figured it out when looking them up. I often have great fun going down the Wikipedia Rabbit hole reading this manga. ?
@Cal The Type 38 was introduced in 1907. The Type 3 was a different Hotchkiss-based gun, introduced in 1914. It notably did not have a buttstock and pistol grip, had much smaller and numerous cooling vanes, and a longer barrel. Both the earlier Type 38 and Type 3 were chambered for 6.5 Arisaka and used 30-round feed strips.
The deranged twin gets more deranged every chapter, but the people around him just seem to adjust to it without any difficulty. Tsurumi was literally treating him like a badly behaved dog... which he lets be honest.