Before we leave the Fedorov, I would like to take a moment to address a common misconception – the Fedorov did not use MG13 magazines. The two designs certainly are very similar, but they are not interchangeable. The Fedorov magazine is a bit smaller, and the locking mechanisms are different. I’ve added a handful of photos of the Fedorov magazine to the Fedorov page in the Vault, including several showing a side-by-side comparison of a Fedorov and MG13 mag.
At any rate, even if they were the same magazine, it would be the MG13 that used the Federov mag, not the other way around, since the Federov was an earlier weapon.