As someone who has used firearms, the bigger issue I have is the heavily exaggerated damage done by these guns.
@Alekhzandr Also a handgun is really hard to aim when you first use it, you need practice, but I'll ignore that. Maybe I would buy into it if the gun had summoned a. 50 cal pistol like the desert eagle and used both hands for stabilization but looks like a standard 9mm. Even if you unloaded a whole clip at that monster, it's not gonna do much unless you hit the eyes.
I live in Canada and people up north despite have semi auto shotguns still worry about a fight with a wolf or bear if you're carrying into a known issue area. These monsters are much bigger and fiercer. Also an AR fires rounds that are meant to pierce as the bullets are encased, not cause big holes in monsters. In the second encounter during the practice area it'd be more realistic if he summoned a Browning M.2 on a tripod. An assault rifle would be better used on human troops and even then I'd prefer an M249 SAW with box magazine as I'm guessing human troops would be forming squads with Roman shield tactics so you'd need the ammo and firing duration.
But I have to honestly don't expect much from Japanese writers when it comes to firearms, even though it'd take maybe a few hours of YouTube to learn.
@The5thSeraph Lolis don't pose any threat to the social dominance of the MC, can act like kids so readers don't want them to be romanced but are accepted to be just as powerful as adult women in power fantasy settings. Key thing here is "doesn't pose a romantic option" as God forbid a manga or anime MC get some action even if they're in a different world. She's basically a pet. The ideal first monster would be a highly intelligent and cunning woman with charm, so someone who can serve as a support role like a secretary, advisor as well as bodyguard. But manga logic go BRRRRR "power of friends better!"