Having shot muzzleloaders for years before straying into CAS, I can confirm that the American/German crescent buttplate shape requires a different stance, and placement of the butt, than the flat "shotgun-style" buttplate traditional on English rifles ... especially if the crescent is quite pronounced, with sharp points!
![Shocked :o](https://www.cascity.com/forumhall/Smileys/cowboys/shocked.gif)
In fact, I have seen old-time references to differing "national" shooting stances or styles ... clearly attributable to the differing butt styles common in the respective countries. "English Stance" was clearly described to be what is most common today - i.e. with the butt planted squarely on the shoulder, at or below the collarbone. "American Stance", on the other hand, had the butt placed just
off the shoulder, against the upper bicep (with the upper half of that arm at, or very near, horizontal) permitting the crescent butt to cup the upper arm, with the lower point tucked into the armpit.
You will see many Black Powder shooters ... especially if they shoot a rifle with a pronounced crescent butt ... using this stance - often this type of butt placement will be combined with another rather odd-looking thing: i.e. the arm supporting the fore-end is not positioned under the rifle as a "prop", but rather is also extended at or near the horizontal (in some extreme cases I have seen the elbow(s)
above the shoulder). In this stance, the rifle is essentially "slung in a cradle" rather than being propped up ....
While I could never master that extreme stance, I certainly learned that placement of a crescent butt on/around the upper arm was vastly more comfortable (and stable) ...