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My wife and I spoke to Prince Alfred von Habsberg zu Hohenhausen and his wife for 1 hour at the Weekend of Heroes gathering in 2004.
A few of the questions were directly about this picture in your book. (Actually, the picture is a still (1 frame) from some period camera footage.) I asked what was the main SMG weapon he and his men used during the Stalingrad battle, he said "MP-41." I asked if any of his men were issued the MKb 42 Assault Rifles during the battle, he said he knows of none being issued or used in the units he was severing in at that time.
Then I asked about the hat he was wearing in the photo, I stated that the M-43 field cap he had on in the picture was introduced in June of 1943, 7-8 months later than the photo was hand label, he said to me "the photo must have been label wrong and could not be from the Stalingrad battle."
Sidenote: The Volgograd State panoramic museum "Stalingrad Battle" has no captured MKb 42 (or 43 version) Assault Rifles on display or in their collection.
Also, excepted for this claim have not seen one photo or written reference that the MKb 42 Assault Rifle was at the battle of Stalingrad.
As we know, there were only some stray weapons around in January and around 8 000 machine rifles first in July 1942.
So the weapon can not have existed other than as a stray test weapon at the time when the battle of Cholm occured.
The large-scale tests on the troops were carried out not until the spring of 1943, a whole year later, by the SS-division Wiking. 20 000 MKb42(H) was being delivered in April to Heeresgruppe Nord. The results from these tests were so good that three army generals recommended Hitler to start serie manufacture the weapon.
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Some info from around the internet, trustable or not.