I recently bought some old cartridges at a flea market. Among them were some old 30-06 to add to my collection. There were three "first model " guard cartridges, one of the "second model" and a tinned paper bullet blank. Three among them (not the second model guard cartridge) were head stamped FA and a date before the 30-06 was adopted i.e. 1905. One was stamped 6 06. They were all 30-06 length, however. The head stamp had a line through it, as was customary for salvaged cartridge cases used for blanks, etc. at the time.
It appears that that some of the 30-03 cartridges left over after conversion of the rifles to 30-06 were salvaged for reduced load use and shortened. The sources I read, including Brophy, do not mention this or I have not found it, but it is a small point, I am sure. Is this the usual case?
I have never had the opportunity to add a military 30-03 cartridge to my Springfield stuff. I do have a commercial example. The original military cartridges must be scarce in that chambering. I wonder if it is because most were converted for secondary use? I am looking at a small sample, I admit.