Early guns and rifles, say guns we think or hope are pre-1770, sometimes have hammered sheet brass buttplates.
Examples:
Marshall rifle. Seems unlikely a casting would break through at the heel.
RCA 40. RCA means a book called Rifles of Colonial America
It would be easy to make buttplates for RCA 42, 43, 45 from sheet brass. Also RCA 51 and 52. Same with the early Lehigh buttplates. Not saying they were not cast most of the time. Buttplate for RCA 65 would be easy from sheet brass but it looks heavier.
In RCA volume 2 I would not hesitate to form buttplates for the following using sheet brass, and some of them may have been made that way.
Rifles 86, 87, 90, 91, 98, 102, 104, 109, 110,,112, 116, 118.