I'm confused. The M307 is the HEAT, and the M306 is the HE.
You asked earlier about the M306 and M306A1 differences. First 2 left to right are 1945 dated. Far left T22, 2nd from left M306. The 4 on the right are marked M306A1, except the middle 2 were made in 1952 and 1953, whereas the 2 on the far right were made in 1972 during Nam. Even though the M306A1's are all A1's you can see that the ones made in the 70's have extra material above the rotating band.
In the photo of the complete rounds, the two left most cases are assumed to be 1940's manufacture, but have no date on them. The next stage in making a shoulder for the cases is the 3rd from the left, with a primer dated 1948. The last 4 cases on the right are the most recent design for a shoulder, using 3 bulges around the neck. Those that are marked are dated around 53. I've never seen a 1970's dated case.
