Quandery. You need to sight in your AR15 for exo-atmospheric use in low earth orbit. You are a space shuttle trunk monkey.

How do you set up your sights for short range and long range shooting. You job is to disable enemy satellites and point defense for your space ship and station.

Keep in mind, no aero drag and how LEO differs from deep space. Your long range targets are 1k meters out.

You are restricted to mil spec 855 with no guidance systems other than your aim using a standard AR15 and COTS sights.

Go Go Go.

Are you on a treadmill?

You zero for point-of-aim and point-of-impact to coincide at 1K meters.

Any effect microgravity would have on the path of the bullet would be minimal, and would vary based on the shooter's orientation at the time was shot was fired, so it's not worth considering.

That's my guess.

ETA: This assumes the availability to zero in the same environment as the weapon would be used.To zero on earth, you'd need a target that accounted for gravity and height over bore.

Don't worry about sighting just hold the same offset.  Aim 2 inches high at 0m and 1000m.

This is the way I would do it but the hold 2 inches high could work too.

Figuring lead could be tough. Relative speeds would have to be determined.

Don't forget Newton's Third Law or you will be changing your orbit.

I would say unless you were free floating in orbit (250kg mass) that the recoil would not alter the orbit of your shooting platform enough to matter. The shuttle and the ISS have an enormous amount of mass compared to the recoil of the 5.56 round.

Full auto maybe. But not much.

Dealing with the heat from the gun would be a problem. There is no air to carry the heat from the weapon so just a few shots and it could heat up pretty fast.

Be careful not to shoot directly into your orbital path....or directly behind it either!

If in orbit, could you aim your bullet and fire it into an elliptical orbit that would have a period such that it would nail the target on a later orbit?

Shooting very tiny, very fast, practically invisible objects around orbit seems like a great way to have a bad day.