Honestly, this power boost was so jarring it's insane. Like I know he's an engineer, so it wouldn't be inplausible for him to make an ak-47, but it would have been a lot cooler that instead of making straight away, that he started small with basic projectile weapons, like maybe a small crossbow attached to his arms (kinda like the ones you see in assassin's creed) and slowly worked his way up with a lot of trial and error over many years. (Like going from wrist crossbow, to a modified flintlock, then maybe a revolver, and then to a handgun or something)
Seeing the process in itself imo is interesting for me so I would have loved few chapters of him spending time doing that. Then eventually he'd make handgun, but by the time he does he's vsing higher rank enemies who cannot be taken down by guns (Like giant golems, things with super high regeneration like trolls, or things that the bullet just can't penetrate in general), and the handgun ends up being a convenient sidearm that will supplement his swordplay as a way to quickly clear out small fry.
