Sorry but, Rigby is right, replica is the perfect translation.
If these were used for any practise operations is a different thing. In my opinion these were used in schools for EOD personell for example and not used for practise by normal soldiers. I have seen "Nachbildung" objects found together with "U" (Unterricht) stamped material and not together with "Ex" (=Drill, manipulation) stamped material.
Drill (Ex) material may be different manufactured than "Nachbildung" / "U" stamped items. The latter are made like a live object wut with the explosive replaced by inert material. Drill/Ex material is sometimes manufactured more rigid than live material, has sometimes special handles, etc.