Shumway showed a few early American guns, look to be 18th century anyway, with variations of the semi-oval and rounded or "beavertail"cheekpieces. Don't know the page or gun numbers from RCA off the top of my head, but there are at least two in Volume 2 as I recall. One is that magnificent rifle with the Virginia Valley looking patchbox (4 petal "edelweiss" finial) and floral wire inlay around the breech that was in the Windsor Castle collection, which Shumway attributed as "maybe" York County, but possibly from other places as well.
In the 19th century they turn up occasionally on fullstock flint guns made in Virginia, including what is now West Virginia, Tennessee, probably other places too. There were a couple (I think one of these may be one that Dennis was referring to) such iron mounted guns listed for sale on this site a few months back. Whisker shows quite a few with rounded cheekpieces in his "Virginia" books - when done right, they are quite beautiful.
Guy