@Hell_Satan,
I never said it had to just be his rifle, I said tech in general, that means everything ambiguously included under the term "tech" to include his nanites, suit, drones, whatever the A.I. Iris can help him with, etc. There's also the possibility she could've provided more ammunition, maybe not infinite amounts, but more. Still, all the technology at his disposal.
In other stories like this:
https://mangadex.org/title/41850/ihoujin-dungeon-ni-moguru, and https://mangadex.org/title/22017/manuke-na-fps-player-ga-isekai-e-ochita-baai come to mind, the MC's are limited to the technology they bring with them. Even in Ihoujin Dungeon ni Moguru's case when the MC makes a contract with a goddess, he's still limited to using his skills and technology so far. I haven't read the novel so I don't know if this will change later. Same with FPS player in another world, he's limited to whatever he had in the game before transporting to the fantasy world. He can't even use magic, he can't even be healed by magic because he doesn't have magic. Of course, the mechanics in all three of these stories are different, just the core that they are modern soldiers in a fantasy realm is similar. I just thought it would've been interesting for him to go without magic for a while, or at least not from having no magic to being uber with it so fast.
Either way, I'll read to see what happens. It just would've been nice to get a third advanced soldier in fantasy land type vibe, that's all.
As far as mental imaging goes. After rereading that page, I now think that was the MC deducing that from his experience playing video games. Deciphering who was talking in that conversation was probably what confused me.