It cant be done with a stock rifle. The rifle was designed to be loaded only when the poop hit the fan, so they went with 5 round striper, with a magazine capacity of 4. the top one was to be rammed into the chamber for killing nazis and other undesirables.
To get a 5 shot magazine, with standard sized ammo, you would need to change the spring system for the magazine. that would possibly help.
could try an enbloc clip arrangement to really get 5+1 capacity.
The most obvious way would be to change the cartridge we all love. Youd have to remove the rim at a minimum. Ideally youd make it a rimless round, and reduce the case diameter till it was only .10" larger in diameter then the neck diameter. That would be the best bet. as that would allow use of a permanently installed chamber adapter and not need a new barrel.
But there is no real point in hopping the capacity up. This is a real mans weapon. It was given the ability with heavy ball ammo, to perforate 3 enemies at 1000 yards. And at that range it would probably mess up a oil drum.
At short range with any kind of expanding bullet, it kicks major ass. the only animals that may be too much for the barnaul 203 grain soft points may be alaskan and canadian grizzly type bears. Though the russians use that ammo for their big bers that are an average 700 kilos.
so it could be done, at great expense. you would not gain anything in the long run. However, you could extend the magazine for more capacity, but why ruin a good rifle.
