IFF i understand correctly, you need to do calculations on single record and then save it to another CSV file. For that read a row in a while function and do calculation on fields on that particular record and then save the result in another csv file all in one while function.
its a simple task.
Isn't MG3 derived from MG42 and improved over old design. Many still use it around the world as GP machine gun. It still works exceptionally well in good hands.
If it ain't broke, don't fix it is the reason it hasn't seen much improvement as it is already well engineered.