In WWII, the allies experimented with converting Lee-Enfield rifles to semi-automatic firing weapons. The US already had the semi-auto M1 Garand, and so didn’t have to do this. And the Germans tried to invent semi-auto rifles from scratch (the Gewehr 41 and 43) but didn’t adopt them.
But did the Germans ever try to convert the old bolt-action Kar98(k) rifle to a semi-auto version?
Not the same as conversion to automatic fire like the Pedersen devices designed for the Springfield 03s, but the Germans did attach the 20-round magazines from MG13s onto their gewehr 98s
Significantly, those Pedersen devices were infamously scrapped after WWI, but in the desperate early days of WWII, the Marines spot-welded magazines onto their Springfields rather than order more Pedersens.