Gun barrel came from 1.35th ESCI Soviet T-72 tank kit, given its non-tapered barrel appearance, I designated gun as smooth-bore Panzerabwehrwerfer (PAW) or antitank projector. PAW guns used sabot artillery rounds (warhead wrapped in armor sleeve), thus able to use a High-Low pressure propellent concept. When shell leaves barrel, sabot sleeve auto-separates from warhead. Control of propellent pressure enable construction of non-tapered gun barrels, thus longer and lighter gun could be made. Sabot - en.wikipedia.org/wiki/Sabot

Nevertheless, physical limitation on gun barrel design exists, specifically Gun Yaw and Barrel Wrap problems. Gun Yaw is swivel effect imparted to gun once shell leaves the barrel, thus tank crews had to wait until momentum ceases before firing next round or else target solution will be off. Barrel Wrap is heat build-up from continous firing within the barrel, thus bending its linear design. In both cases for WW2 tanks and tank destroyers, longer the barrel, more pronounced the Yaw/Wrap problems. Roll, Pitch and Yaw : Fire Control Problems and Mark 1/1A Solutions - www.navweaps.com/index_tech/tech-074.htm

Inset 1 : Combat experience shown that Stug III 7.5cm StuK 40 L/48 gun was not sufficient to punch through late-war Soviet tanks such as IS-2 and uparmored T-34/85 tanks. Hence, German Panther tank's 7.5cm PAK39 L/48 gun was mounted into sloped hull Panzer IV chassis, called Jadgpanzer IV. It was a formiable weapon capable of knocking out almost any Allied armor. Photo depicts Jadgpanzer engaged in Eastern European street battles circa 1945 by-passing dead horse carcass and wreck vehicles in background, note large ballistic armor block in front glacis plate to deflect incoming enemy rounds. Jagdpanzer IV 75mm L/48 (1944) - www.achtungpanzer.com/pz10.htm

Vehicle nicknamed Guderian Ente (Guderian's Duck) due to its low silhouette and stubby Saukopf gun mantle. Heinz Guderian was German general who invented Blitzkrieg battle tactics of combined arms attack of coordinating air, ground, mechanized forces onto a localized target to penetrate, outflank, envelope enemy formations. Heinz Guderian - en.wikipedia.org/wiki/Heinz_Guderian

Rollover : ( Rollover JPG link ) | Panzer IV hull from 1.35th TAMIYA Mobelwagen self-propelled FLAK gun, large rear idler from 1.35th TAMIYA Brummbar assault gun, Schurzen armor skirts from 1.35th TAMIYA Jadgpanzer IV kit. Rubber tracks painted TESTOR Military Brown, dry brush in TESTOR Chrome enamel paints. Tank camouflage of soft-edged Forest Green and Red Brown acrylics painted with air brush. Water canister from 1.35th TAMIYA SdKfz 231 8-rad armored car. Spare roadwheels and tracks from 1.35th ITALERI Panzer IV tank. Schurzen mounts from 1.35th Jadgpanzer IV (A) kit, only installed skirts in middle section since plates at both ends of vehicles were routinely torn-off due to collisions with buildings and scrapes with foliage. Display base made from precut wooden product with surface details cut from cobble stone plastic sheet.

Inset 2 : With superb effectiveness of Jadgpanzer IV, main gun upgraded to 7.5cm PAK39 L/70 gun. Its longer barrel gave artillery shells greater velocity since compressed gas was contained for longer propelling duration. However, longer barrel also impeded vehicle handling, along with compensation for gun yaw and barrel warp problems. Jagdpanzer IV Munster - www.wargamer.com/Hosted/Panzer/munster/JagdpanzerIV2/index.html

This Jadgpanzer IV variant also called LANG (German for Long) version, photo depicts Jadgpanzer with bolted-on spare tracks as appplique armor and schurzen, its rear engine hatch opened for maintenance. Personnel standing in front with arm band seems to be from local Nazi paramilitary units (ex. Hitlerjugend/Hitler Youth, Sturmabteilung/Brown Shirts, or Volkstrum/Home Defense). Jagdpanzer IV 75mm L/70 (1944-1945) - www.achtungpanzer.com/pz10.htm