Good point and I should have mentioned that I am interested in freehand or soft hammer reduction of small cores in order to contrasts with bipolar or hard hammer. Most studies with bipolar have been conducted with hard hammers. Behm (1983) is the only experiment with soft hammer reduction of small cores that I am aware.

There is a site in northern Switzerland where extremely small chert nodules, only  a couple of centimeters in diameter, have been extracted/mined during the Neolithic. The archaeologist (and knapper) working on the assemblage, Kurt Altorfer, has been experimenting how these very small nodules can be worked, resulting in cores, flakes and débitage that closely resembles the prehistoric material. His work has been published, but only in German in K. Altorfer/J. Affolter, Schaffhauser Silex-Vorkommen und Nutzung. Beiträge zur Schaffhauser Archäologie 5 (Schaffhausen 2011), pages 67-74. „Rekonstruktion der Zerlegungstechniken“.

William, I think mention of end product is important. Also, what is your criteria for small cobbles/cores? In cobble reduction you normally have initial hard-hammer reduction in order to produce platforms that then can be struck by soft-hammer methods (limestone hammerstone or antler billet). Most of the lithic reduction in Louisiana, east Texas, and southern Mississippi was done on Pliocene/Pleistocene gravels averaging 6 - 10 cm that were roughed out using a hammerstone prior to soft-hammer reduction. Also, be aware that some lithic material types require a certain angle of attack to be used during soft-hammer reduction that mimics and is indistinguishable from bipolar reduction. Then there is split pebble technology that is more effective than bipolar technology in producing thin cores from cobbles that can then be reduced into bifaces.