Firearms of the American West 1803 - 1865 on page 231. is a picture of a .75 calibre, appears straight octagonal barreled rifle, made by Krider, Philladelphia, "perhaps for western use". On the cheek piece, a silver oval cartouche is inscribed "Presented to/Capt. W.H. Owen/by/Major Chevallie/April 9th 1852"
This rifle is not really different in appearance from ANY English Sporting rifle of the same period. It does bear 2 forend wedges, but has what appears a Penn. trigger guard with middle finger rest, English lock and breech, with a drip rail & DS triggers. The barrel appears to be about 30" long. It actually looks very similar to Taylor's Lang or my .69 rifle by Taylor. Had it been noted to have been make in England, I would not have been surprised. Thus, the plains rifles 'of the day' were indeed of a variety of shapes and sizes.
Of course there are a lot of generic "western" or "plains" rifle pictured in this book. It is well worth collecting. As well as the same period, 1803 through 1865, handguns, pistols, revolvers, contract guns and rifles, muskets, smoothbores and "Indian Guns". On the same page as the afor mentioned large calibre rifle, is a picture of a 13 pound, 34" bl. 58 calibre Leman full stock "Improved Bear Rifle" (so stamped). With only a 34" bl. you KNOW it is of decent girth, being 13 pounds weight.