https://www.youtube.com/watch?v=yM3cwvw8TPE

what I have heard about it that the barrel was set back exactly that the 7,62x39 headspace in the original 303 chamber. dont know how exactly this was done but I think its better to set the barrel 1 to 2 mm more back then necessary and reaming the 7,62x39 mm chamber in the common way.
that is the easy part

here is a vid with the original magazin for the 303 using 7,62

https://www.youtube.com/watch?v=Dp3RFZx4ayk

allways possible to get another magazine into the action but maybe some work

I would build a sporting rifle in the style of a jungle carbine but without any military stuff on it and with hunting sights.

have a similar project with a carano and an ex 7,62x54R barrel for a dandy stutzen. magazine will be a CZ 527 magazine that fits into the carcano action.