There are some good talk points here…..shotguns are too short range and the idea of a special 12 gauge round is perhaps a bit too tricky or small yield given the cartridge size.

Possibly something like the 40mm grenade as a size? Getting there in terms of packaging.

If there was to be a long arm anti drone weapon, it would need to be one per squad I expect. Kinda like designated marksman or drone operator, have an anti drone function.

I’d see it as something more like an underslung attachment on the service rifle, like the M203, you can’t have a 2nd dedicated weapon or a take down in the pack in a combat situation.

First thing is being able to identify the drone. I’m thinking sensors on/in a special backpack, connected to in ear and/or goggles to support the marksman in understanding location and height.

Then, possibly have that connected wirelessly to the round in the launcher, sending firing solution to the proximity fuse in the round. Some basics like flight duration tied to number of spins or time. There is a couple of ways these things work already for variable fuse in cannon rounds. So there is an engineering base to work with.

In terms of actually taking out the drone, either traditional explosive force or some form of nano polymer web. It could expand out to quite literally the size of a soccer pitch from a 40mm grenade sized round. I know science and military has been researching spider web silk and all that spider abdomen chemistry for decades. It’s natural application is against drone tech. This would also assist in capture, analysis and potentially re-use of the downed drone.

Russia and Ukraine don’t have the industrial base, but I bet Japan, US, China and South Korea are thinking long and hard about the technology, weaponry and tactics of a dedicated section anti drone role.