Finding isekai that gets the sniping right is harder than hitting a thousand-yard shot in a crosswind. A lot of the genre leans on magic-enhanced rifles or system-assisted aim, which is fun but scratches a different itch. The ones that stand out for realistic tradecraft tend to be on the grittier, more survivalist side of the spectrum.
'Gun-Ota ga Mahou Sekai ni Tensei shitara' has its moments, especially early on when the protagonist is basically just a guy with a bolt-action in a medieval world. The focus is on logistics—making gunpowder, dealing with barrel wear—more than pure sniping, but the technical details feel researched. For pure long-range artistry, I'd point you toward 'The Sniper's Reign in Another World', a web novel I stumbled on. It spends chapters on wind calls, mirage, even the psychological toll of the stalk. The protagonist isn't overpowered; he's just terrifyingly competent and patient.
Honestly, you might have better luck in military or progression fantasy adjacent spaces. Books like 'The Martian' for the problem-solving vibe, but set in a fantasy context, are where the real precision-oriented narratives hide. The classic isekai sniper often becomes a cheat-skill gimmick by volume three.