While i have not done any professional shooting, I do own a Kar98k and Mosin 44 and i notice huge differences with the clip loadings. Even with very bad turkish ammo clips, the mauser never has any cartridges bind while loading and the magazine can be charged in one motion. I several types of clips for the mosin and they are all terrible. Mosin clips have a "top" and "bottom" because they are rimmed and the magazine is single stacked. The metal clips will flex when you are pushing in rounds and they will bind. My rifle reloads are about as fast as in game, if not slower. A lee enfield isn't as bad because it's a double-column magazine and properly loaded clips don't have a "top" or "bottom." But the mauser will load faster than any of my other guns.
It is my understanding that the G43 was issued with a few spare magazines and ammo on clips. It would be hard to model said reload given the current game engine i suppose. But i really wish i could pick up K98 ammo pouches when I'm out of ammo.
IIRC PPSH's were issued with only 1 drum after '43 or so, with 4-6 stick magazines. The drums jammed, were cumbersome to carry and load, but held a lot of rounds, so in a firefight one would have a good amount available to start and have reliable reloads should they be needed.
One could also try reloading belts and magazines from similar caliber guns- like emptying walther magazines to fill an MP-40 magazine- but such a system would be long, cumbersome, and limited.