Taylor describes how this is done, and my photos show it also, that is, the well-defined target so you can aim exactly. Just shoot for the middle. T*O*F, I have already cut the horizontal string with another rifle. See Candle Snuffer's post nearby concerning shooting Olde Eynsford in a flintlock rifle. There I posted a photo of a target I shot at 100 yards with my .58 fullstock flintlock Hawken I built. There is a faint pencil line at the middle of the paper target, vertical and horizontal. My first two shots went through the same hole and would have cut a horizontal string there, and the fifth also would have hit it. My wonder is not that I can shoot so well but that all the shots don't go into the same small group. I think it must be the cast lead balls. If I mike them for size, they are not round, and this must be one of the factors that results in large groups. That and holding the rifle and taking up recoil exactly the same each time, let alone seeing the sights and target. I will shoot horizontal strings when I can get to my range.
Yesterday I went to Ogden to meet with the Fort Bridger Rendezvous Association board of directors to offer them my Bridger rifle for next year's (2014) Fort Bridger Rendezvous rifle raffle. I explained how I built the rifle and in case anyone asked "how does it shoot?" I wanted to offer proof. My photos of this string cutting at 100 yards was that proof. They will let me know if they want the rifle.
Others of you can also cut strings like this. Maybe start out at 50 yards, practice up and amaze your friends.