Ron5 wrote: can the lead bit be embedded in the propellant? Maybe with a composite container instead of brass?
To a degree (only), yes. In a drive to get a longer bullet (better ballistics) a French study took 106 pages to conclude that, but they nuanced the case a bit further (I am sure all of the below will emerge with the new US 6.8 mm GP becoming "observable"):
"Of course, if one was to adopt a new round, it would be highly advisable that this new round case
geometry should allow (from the beginning) the easy use of a light polymer (or composite) case.
A polymer case (with a light alloy case head) could:
• be tailored so that case capacity exactly fits the powder load and avoids free volume,
decreasing shot-to-shot dispersion and improving internal ballistics, • reduce the heat transfer from the cartridge to the chamber due to their low heat conductivity, • reduce the weight of a given round by ~30-35% compared to conventional brass cased
The cartridge described above, with a composite case and a slightly greater body diameter
(~11.2 mm) to account for the internal volume loss due to the polymer body, is expected to be no
heavier than the current 5.56 x 45 mm SS-109. "