One of the advantages of a tank over a self propelled gun is the ability to fire in a 360 degree arc. While firing forward is the typical use case, firing backwards can have some unexpected challenges. For example, the low bore axis of the L-10 gun and protruding muffler on the T-28 were a bad combination.
"Testing the L-10 gun in the cylindrical turret shows that the gun depression when facing the rear can be, at best, 0°, unlike the -4° or -5° that the gun allows for. The state of the L-10 on the provided prototype of the conical turret is the same."
"12 shots were fired at an angle of depression of -3° from two vehicles. While shooting towards the rear, the gases damaged the deflection plate above the muffler. The muffler on one tank shifted by 15 mm. In one case, the plate was hit by the shell. Damage from gases was also observed at elevation angles of +2°. Given the current design of the deflection plate and muffler, the L-10, characterized by its low bore axis, cannot shoot backwards not only at an angle of -3°, but even +2°.
In addition, when shooting across the side air intakes with an active fan at a depression angle of -3°, the fan slowed down for the duration of about one second."
Maximum gun depression (-3° in at all other angles vs +4.30° when facing directly to the rear).
Diagram showing the arc in which the gun depression is limited (20 degrees to each side).
Damage to the muffler as a result of escaping gases.
"History of the T-34 tank" Memorial Museum Complex, Documentary Historical Collection #2