Hyperspace makes you the tachyon bullet, though.
Thanks for the reference, I can now think about it easily. Hyperspace travel doesn't just let you teleport in normal space, it makes you teleport across reference frames.
So let's say instead of A firing an instantly lethal bullet at B, A fires themselves to where it looks to A where B is. Since they also teleport across reference frames, they won't emerge from hyperspace where they originally observed B to be. The only way to ram B with their hyperspace ship would be to teleport across to B's reference frame, in the process murdering the grandfather paradox along with B.
However, intriguingly, B can see A arrive before they see A leave. As long as it remains hyperspace and not hypertime travel, this can't result in any paradox. Since B can see A arrive before they witness the departure, A can witness their own departure. They can't interfere, however, as any signals they send back to the departure point have to take the time to travel back. If they try to use hyperspace, the reference frame teleportation will take them back to slightly later in their original reference frame.
Or, from the reference frame formerly known as A, a hyperspace cannon fired at where A thinks B is at eight seconds would be seen to appear by A roughly seven seconds later. By this time B has moved some more. A can solve the equation and lead the shot the necessary amount, but it will always work out to be exactly like shooting B with a beam of light.
This is one of the reasons not to believe in normal wormholes. Since they don't transform reference frames, they can lead to grandfather paradoxes.
Also, an actual tachyon pulse would appear at the target and race back to the tachyon lance, charging it, whereupon you decide to fire it and it discharges again. While this seems cool, it's just the amazing ability of the human brain to imagine impossible things. Your brain is (classically considered to be) entirely made of physics, yet it can consider decidedly unphysical and impossible events. I dunno, I'm not sure how that's possible. Even more cool impossible things: the tachyon pulse would start at its greatest penetration and then rip its way outward on the way back to the lance.
This can be got around by having very fast tachyons, that go backwards in time a negligible amount. Equivalently, a very slow negative temporal speed.
Come to think, this is sort of how a tachyon pistol would work too. Actually if A sees B killed at four seconds on B's clock, A would see a bullet appear in B, and fly out backwards, and then A would have to catch the bullet in their tachyon pistol or the universe would blue screen. Unfortunately this still wouldn't work because entropy isn't symmetrical. When the bullet arrived in the barrel, it wouldn't be able to collect its tachyon explosion into tachyon gunpowder. It would become more ordered, yes, but there's nothing forcing it to that particular order. Which in turn means nothing is properly arranged to propel the bullet out of the barrel.
I found this out thinking about reversing time. Imagine a log burning. If time is reversed, the smoke will fall instead of rise and absorb energy instead of releasing it and become more ordered rather than less. But the whole point of entropy is that the smoke can't know what it was before it was burnt. It could be any number of carbony compounds. It won't turn back into a log, it will just condense into random stuff. It will try to maximize enthalpy instead of minimizing it, meaning it will probably be a chunk of what we'd call hyper-sensitive explosives. And not in the shape of a log, just whatever ground it happens to land on.
Of course maybe it will still rise because gravity may also be reversed and Earth would be quietly dismantling itself. I'm not sure, I'd have to think about it some more.
But if time were reversed, people wouldn't start walking backwards and forgetting things, they'd just all keel over dead. Individual processes reverse, not systematic processes. Reversed, they don't work together the way they do forwards.
Okay I thought about gravity some more. There' two competing theories, the quantum and the Einsteinian.
In the first, gravity force is the result of absorbing gravitons. In reversed time, it would be a process of gravitons streaming in from everywhere towards masses, and you'd feel a push downard from them if you got in the way. (I think. You feel a small pull every time you emit a graviton, by Newton's Third on the pull you'll cause on the target. It cancels out from emitting them in all directions, though. In reversed time, you'd instead feel a small push when you absorb them, going the other direction.)
In the second, gravity is the result of space being curved. In reversed time, space has the same curve.
In either case, stuff still falls toward Earth. Just, in reversed time, people float and smoke sinks in air.