the 401 would not a good rifle for a kid, its very, very heavy. maybe the smaller cartridge rifle's up to 351 WSL?
any game bigger than roedeer need an energy over 2000 joule at 100 meter to be legal here and iirc this is the same minimum on moose in sweden today. so this old rifles are more or less worthless in sweden now.

the 401 WSL is in fact a 41 super magnum and the 414 super magnum brass by starline is the best solution for making it. http://www.johannsen-jagd.de/data_de/katalog/sammelseiten/Huelsen.pdf
the case have to be cut for 1,5mm and the rim have to be turned down and its ready.