I know what Grandveneur means, when you load the next round from a double row magazin the cartridge move in 3 dimensions. on the way into the chamber there is one moment when the cartridge with a rebated rim can slip under the bold head. the feeding can be made trouble free but it needs alot of experience and the time, maybe similar to making a double rifle.
feeding from a single stack magazine is no problem at all like the .50 Beowulf in a M 16 magazine.
https://www.youtube.com/shorts/Oxfz7orosiI