Base Chassis

172 Ausf. J chassis were delivered from Nibelungenwerk (NiWerk) for Sturmpanzer production, since 166 Series 4 were produced and produced in a different facility than previous versions it would seem reasonable, since no previous version chassis would have been around to use instead, that all series 4 were built on Ausf. J chassis.

Return Rollers

Because of what I mentioned above all Series 4 Sturmpanzer would likely have had steel return rolls (all J’s had steel return rollers). Having 3 return rollers is however another matter. The 3 return rollers per side was introduced into PzKpfw IV chassis production in December 1944, since the last shipment of chassis from NiWerk were received in November it seems improbable that any Sturmpanzer had 3 return rollers per side and I am not aware of any photo evidence to the contrary.  

Extended side hull

I would like to see and example of a Sturmpanzer with extended hull sides but also think this is unlikely. Extended hull sides were introduced into production in October 1944, again final deliveries of chassis occurred in November 1944. Although I do not know the time it takes run a panzer IV hull through the production it seems that the hull sides would be required at the very beginning of the assembly and this change would not be visible on chassis leaving the factory in October and possibly November. I am not convinced that this feature was ever featured on the Sturmpanzer. Actung Panzer #4 shows a drawing of a Sturmpanzer with extended hull sides but I am skeptical that this is based in fact. They also show the rear coupling for tow bars on another drawing but that feature was not introduced until December 1944. The tow bar was an item to be back fitted but I have found no evidence of any Sturmpanzer with it in place.  

Exhaust

Flammentoeter mufflers where introduced in August 1944, so it would seem likely that some of the Sturmpanzers would have this feature. I know of only one photo where Flammentoeter are visible on a Sturmpanzer though and this is a example photographed in the Ardennes, December 1944. There are later models that do not posses this exhaust type, it would be interesting to know how prevalent this feature was.

Shurzen

All Series 4 Sturmpanzers should have left the factory with solid shurzen in place, even very late Strumpanzers show evidence of shurzen. There is nothing that I have seen or read that would indicate that the practice of installing shurzen was ever discontinued once started.

Steel Wheels

Steel wheels it appears were introduced with the Series 4 production; they do not however follow a consistent and discernable pattern. One of the first Series 4 produced that can be seen in factory photos shows an all steel wheel setup but there are also instances of all rubber wheels and then some very late Sturmpanzer with only 4 steel wheels per side. It seems to me that they began with the idea of all steels wheels and then shortages (or maybe weight issues) caused them to rethink the strategy and reduce this to 4 per side. The occasional instances of no steel wheels being available could have caused the odd no steel wheel sample.  

Sturmpanzer Befehlswagen

I have no data on these other than photo evidence shows that both Series 3 and Series 4 Sturmpanzer had a befehlswagen version.