Receiver variations have never received a lot of attention here.
I have had 2 semi-low walls. Both of mine looked like they received the next pass on the mill from the one bones92 found.
I thought for years that this was a 5.0.1 I finally decided that it was a semi too.
1941 is a very interesting year to collect as the Soviets became quite busy making rifles to counter the German invasion. At the beginning of 1941, Mosins were built just like they were in the late 1930s. By the end of that year, most of the features we associate with wartime production were in place.