Your vent hole on a flintlock. I came across an interesting disscussion on another site and thought it would be interesting to see wht you guy's do.

I pick my vent when I don't I get F.I.P.'s. I think it helps keep the liner clean thus ensuring a spark transfer from the pan to the charge. I also bank the powder to the outside of the pan. Basic geometry dictates that would be the preferred place for the prime IMO.

I did a little youtubing and found this Siler lock demo in slow motion. Be patient it is in Super Slow Mo
http://ca.youtube.com/watch?v=GzgVnH6uEP0&feature=related

and another
http://ca.youtube.com/watch?v=mLLHXwoClyo&feature=related