think you mean this vid?

https://www.youtube.com/watch?v=ul690I9Ba2Y

new also to me but I would think its collectors stuff today. it dont survive the last decades and by the way it was build I see no advantage about other slug designs. this are just common elements you find on a lot of other slug.
maybe the ammo just shot very good in this special gun but its common that slugs shooting fine in one gun and fail in the other.
and what they are doing its not the proper way to test a cartridge, imho!