I too have wondered at what date the headstamps changed. I understand the REM-UMC headstamps began in 1912 and were continued until 1934 when Remington purchased Peters. I understand the R-P headstamps to have begun in 1960 or so. Between, 1934 and WWII, I suspect that headstamps may have varied depending on the round. I suspect that the REM-USA 30 USA was continued at least until WWII and the Peters headstamp was used primarily after WWII through 1960 and after 1960, both R-P and Peters were used regionally. I would expect that a plain brown box would be in the teens, then the white boxes were used through 1934, then multi-colored boxes were used but then most likely after WWII. This is all LONG before my time so it is all based on my findings in the last 30 years or so. It will be interesting to hear what others have learned.