That's certainly not impossible at 600 fps... I remember one time I was out with my dad shooting .45 military ammo. I was standing off a bit to the side and the sun was low on the horizon. I could see that golden streak going downrange every time he fired.

Never seen it from behind the weapon though, there's usually too much smoke and flame obscuring that perspective! <img src="images/graemlins/grin.gif" alt="" />