Flash timing

I have a 580exII. Can I set the flash to go off when I open the shutter, as opposed to when the shutter closes? I am trying to capture muzzle flash. So I have a 1-2 second exposure for the gun, then the flash exposes the subject. When the flash fires after, they have to reposition themselves exactly as they were before they shot, or the gun and flames don't align.
I've looked through the instruction book but don't see anything about it. I am using manual flash and camera modes.

First curtain sync is the normal mode. second curtain sync is in the custom function menu and is controlled by the camera connection or via certain off camera triggers with all the pins connected

I'm trying to figure out why you would want a 1-2 second exposure to capture a gun and muzzle flash with... flash.

The muzzle flash is a light source that lasts a fraction of a second. Your camera flash is a light source that only needs a 1/250 shutter speed.

Your challenge is not syncing the camera flash with first or second shutter curtain. Your challenge is syncing the camera flash with the muzzle flash. I can't see how a slow shutter speed helps with that.

What is a muzzle flash? I've never come across that before.

It sounds like the OP is trying to make a photograph of someone firing a gun with the flash to illuminate the shooter and gun and the time exposure is to give them sufficient time to fire and let the muzzle flash register on the image as well.
The rear curtain sync firing means the gun recoil is placing the gun out of alignment with the muzzle flash because the rear curtain sync is capturing the shooter and gun after the muzzle flash rather than before.

My suggestion, since its manual flash, is to trigger the flash independent of the camera shutter.

i.e. open the shutter, manually press the fire button on the radio trigger to fire the flash and tell the shooter to fire the gun when they see the flash. Normal human reaction time with cause the muzzle flash to be a 1/4 second or so after the flash fires capturing the shooter and gun.

The flash probably isn't firing after (Second-Curtain Sync), you're just not synching it to the gun. What's your setup? Do a search on high speed photography and you can buy or build a trigger that will fire your flash when the trigger sees/hears the shot from the gun. You can build the microphone type or the laser type trigger. With a programmable delay, you should be able to fine tune it to achieve the shot you like.

I'm guessing that gun recoil is the major culprit here. When the muzzle flash appears, the slug has already left the barrel, the force that causes recoil has already occurred and the barrel is already moving. This is going to be worse in a handgun than a rifle.

There may be solutions, but the OP needs to tell us more about how he is attempting to sync the gun with the camera.

dmward wrote in post #12913790
i.e. open the shutter, manually press the fire button on the radio trigger to fire the flash and tell the shooter to fire the gun when they see the flash. Normal human reaction time with cause the muzzle flash to be a 1/4 second or so after the flash fires capturing the shooter and gun.

This is one way to do it but it needs dark room as the shutter is open fairly long time.
If you want to play around there are few other ways to think about.
I did this kind of test shoot few years ago with DIY sound trigger. Sound trigger was triggering flash unit while shutter was open for few secs.
It can be done manually as well as explained above. I just wanted to make it more automatic and get it right every time.
If you use sound trigger, you dont really need a timer to adjust the delay. You can do it by moving mic away from the gun. As sound travels so slowly 0.34 meters gives you 1ms of delay, 3.43 meters gives you 10ms of delay and so on. Of course digital timer would be cool but there are other ways to do it
Outside in bright conditions this gets a bit tricky. Then you need to trigger the camera instead of flash. Depending on camera models shutter lag is at least 60ms so I think the delay is too long to capture the muzzle flash if sound trigger is used. When camera is pre focused and in manual focus and the mirror is locked up, you can minimize the shutter lag.
This could work with triggering mechanism attached to gun trigger and then use timer to adjust the delay if needed

Okay so sync it to first curtain. Thank you!
To answer the question above, I need a 1-2 second exposure to capture a single shot bolt rifle. The way it has been going (flash firing later) I would take the shot, say "fire", the subject fires the shot and the muzzle flash is captured, then he would have to reposition the weapon to it's original position before the flash fires exposing him. I'll try to post some examples of this method but I can't seem to post to photobucket anymore. :/
Thanks for the help though, I'll re-sync to the proper curtain.

Curtis N wrote in post #12913984
I'm guessing that gun recoil is the major culprit here. When the muzzle flash appears, the slug has already left the barrel, the force that causes recoil has already occurred and the barrel is already moving. This is going to be worse in a handgun than a rifle.

There may be solutions, but the OP needs to tell us more about how he is attempting to sync the gun with the camera.

That's how I imagine the scenario in my head. The shooter and gun are firing straight ahead. When the gun fires, the flash from the muzzle is bright enough to register in the picture. Then the flash eventually fires freezing the barrel of the gun at an angle different from the muzzle flash.

The easiest way would be to make a composite of different pictures blended in Photoshop. The cheapest way would be as David stated above, lower your flash power and hope and pray it works. This sounds dangerous, though...multiple people, firing guns in the dark. Are you firing blanks or live ammunition?

Edit: Apparently, I typed too slow. So you actually set it to Second-Curtain? Because First-Curtain is the default.

Yes that is the ticket! My flash was set to 2nd curtain already. I must have been playing with buttons and didn't realize what I pressed.

So the new plan is to change the shutter speed to 1/2 second, have the shooter ready with the trigger already pressed, tell him to fire when he sees the flash, and hope to catch the fireworks every time. If need be I can just make the shutter speed longer. If the sun is down, any movement they make after the flash shouldn't matter as long as the gun is in the same place for both exposures.

This is what I was getting with 2nd curtain. They are mostly out of focus, as I was still dialing in the correct power when I realized it just wasn't going to work. That said, I was able to capture the flash every single time with single shot weapons (.357 magnum and 12 gauge shot gun). you may also notice their finger is off the trigger, as their exposure was taken up to a second after they pulled the it.