Here's one from the American Museum of Natural History:
(It is about 43" long, highly reflexed in the middle, and the string is on the wrong side).
BOW
NORTH AMERICAN ETHNOGRAPHIC COLLECTION
Catalog No: 50.1/ 7363
Culture: HIDATSA
Locale: ND, DUNN COUNTY?, MCLEAN COUNTY?, MERCER COUNTY?, MOUNTRAIL COUNTY?, FORT BERTHOLD INDIAN RESERVATION
Country: USA
Region: PLAINS
Material: ANTLER (ELK), SINEW, QUILLS, PIGMENT, STRING, PITCH?
Dimensions: L:109.5 W:13 H:4 [in CM]
Accession No: 1913-53
Donor: WILSON, GILBERT L., REV.
Most of the composite bows that I have been able to get specs on were made from sheep horn or large antler of some kind. They were most often spliced in the middle. The sinew backing was always quite thick, maybe 1/2" thick at the handle and 1/8" thick on the tips?
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