According to:
http://www.radix.net/~bbrown/police_unit_marks.html
"LS.AI" is the unit mark from Allenstein Landjaegerei school.
Book is Schmidtt's "Weapon Technology Teaching Book for the Police Officer" published in Berlin in 1928.
So this could well be a complete training rig!
There doesn't appear to be much of a hole in the barrel inserts. Could they be a group of blank firing attachments, perhaps tuned to create different malfunctions?
Nice! Marc
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.