This seems very silly. It's either a death ray project in a fake mustache or somebody had earmarked a bunch of money that they had to spend before it expired.
But much of the stuff DARPA does seems weird. It’s not about ideas with solid foundation and thorough engineering, it’s about crapshoots that might work and would pay off in some way - often any financially feasible way.
They once put “cats” on guns in hopes it would surprise opponents even just for a quarter second, giving your spec ops dudes the advantage. They tried to create angled guns that could shoot around corners like 20 years ago. All kinds of crazy stuff! It would be a lot of fun to work there, I think.
Not sure how you would build one of those without the stress of the bullet during firing would not damage the barrel.
The IDF got a gun that does this[0] into service in 2003.
A future with having wireless energy transfer everywhere is one where energy is so abundant that we don't mind throwing out 80% of it powering wireless things.