The only reason I think Nagant’s bullets are light speed (without calc stacking) is because All Might is constantly praised and admired for his speed, even surprising Shigaraki in the beginning of the series. It’s highly likely that as the #1 hero, All Might was physically superior to
every hero out there and their quirks. Random high schoolers having legitimate lasers at their disposal and reacting to them at point blank ranges solidifies this a bit. Things like sub Rela/real speeds for high tier pros would make sense, and then there’s All Might. Since quirks are physical abilities and physics play a large role in MHA in general, I highly doubt any quirks would be capable of FTL travel speeds. Even saying All Might is LS for being equal to laser quirks would support my argument well. Deku is comparable to Shigaraki physically at his 45% state and higher with Fa Jin and Gearshift, yet Nagant’s bullets were tagging him from kilometers away, even with precog. I believe that if someone equal to All Might’s speed is struggling with a bullet’s speed, the bullet must be comparable to some of the fastest quirks out there. Shigaraki in his (near) complete state even had a light speed quirk (being radio waves) and at that point, he was at/around Prime All Might's speed. We've seen characters similar to Kaminari being capable of reacting to what they can dish out, like Star catching the plane lasers and avoiding radio waves and such. To avoid going on forever, I think Nagant's charged bullets are light speed and should be treated as such when calcing feats, the current rating of Rela is alright but I just think they're faster is all, especially since Star isn't on Prime All Might's level and she was performing Rela+ reactionary and travel feats when faced with light speed attacks. (sorry I yapped so much, I'm a little nuts
).