You have a better eye than I do. I though they were just aluminium tubes.
Thanks for the info.
Do they use bullseye for the filler?
Likely depends on what's available. Powder from pulled shotgun shell cases is common [source for primers, too] and homemade powders using potassium mitrate/saltpeter, [stump killer] finely ground ammonium nitrate and or swimming pool chlorinator calcium hypochlorate [HTH/*Shock*]mixes.
Probably not. But very similar adaptations turned up in the former Portuguese colonies in Africa until AK47 ammo became commonplace. Back then, [circa 1975-'80] shorty single-shot shotguns of around .410 caliber using the battery call cartridge cases were still seen, and it's a likely bet that those turning out such items in Portugal today had experience with them in that previous setting.