Overwatch 2

The basics: You have to build charge with your primary fire . You see a number in the middle of your aim reticle going up. This is your charge shot. Bigger number more damage. Hit to shoot a high impact shot that consumes the stored energy. I found that most times a charge shot 72+ is plenty for a kill shot when hitting the head.

The achievement is simple enough you must pull off a charged railgun head shot while using the power slide move .

These are my tips to make this a little easier:

* Line up to the SIDE of your target instead of the front
* Slide BACKWARDS

Most people will strafe left to right -- from the side this doesn't matter.
Sliding backwards gave me more opportunities because I didn't have to adjust my aim. It naturally moves toward the head.

Best of luck and keep trying. This is what worked out for me.

Upon charging the Railgun, hang back and wait for an injured squishy to enter your line of fire. While sliding try lightly twitching up towards your target's head. Having a Zarya with Gravitational Surge or a Mei with Blizzard to render opponents immobile will make this and her Ultimate related achievement significantly easier.

Payload maps with long fields of fire (King's Row for example) are the most suitable.

Got this on Eichenwalde on defense at the first choke point.
First, try to make sure your Railgun is charged to 100% (indicated under your reticle). Since it has to be a headshot kill, a 100% charge will make it much more likely to score a kill. A Railgun headshot without a kill doesn’t count.
Second, make sure any enemy shields have just broken, Dva barriers have been used up, immortality fields are down, or anything like that because those will block your chance.
Third, try to get when the enemy team is pushing through natural choke point with your team on defense, so the enemy team will tend to be clustered together in a predictable spot.
Fourth, try to start your slide from back behind your tank, so they can cover for you while you slide in. Your approach makes you very vulnerable to enemy fire, and you don’t want to be killed right before pulling your shot off. The other option is to slide backward.
Finally, mine took like a minute to pop, so I thought maybe I messed it up somehow. It finally came through, but at least it didn’t kick me from the game like some of the other new OW2 achievements have.