While researching the M326 recoilless rifle HEP some more, I came across this statement in ammunition, complete round charts, dated 1954: "Shell may be produced from shell, smoke, BE 105-mm, M84." Ammunition, complete round chart, book 2, artillery ammunition, dated 1961 states: "Shell may be produced from Smoke, 105mm, M84." The M84, of course, is boat-tailed. More modern HEP rounds produced by the USA had aluminum bases and were not boat-tailed so this item seemed quite unusual. As it turns out, there is a document on dtic.mil that explains the development of the M327 (T81E28) 105mm howitzer HEP shell. This document plainly states that this HEP round has a steel baseplate. Also, earlier, experimental versions of this round, the M327, used the M84 smoke shell as their starting point so this round, the M326, was not unusual for its time.