High backlash was noticed in the traverse mechanisms.
Conclusions: the traverse mechanism passed trials.
10: Loading tray
In order to make it easier to move between the loader and breech operator's stations, it is reasonable to make the rear tray corners rounded. Otherwise, there are no complaints about the tray.
The prototype carries the telescopic ball and socket TSh-17 sight with 4x magnification and a panoramic sight for the 76 mm ZIS-3 gun without an extension.
The ball and socket sight is comfortable to use due to the immobile eyepiece in relation to the gunner's eye. A lack of muzzle brake improves the conditions of observation after a shot.
Trials showed that after 40 shots the sight calibration offset is negligible.
12: Fighting compartment
Trials of the fighting compartment showed the following:
- There is no access to the air valve of the recoil brake through the gun mantlet, which made it difficult to measure the amount of remaining hydraulic fluid and makes it impossible to release air in case of short strokes during firing.
- The gun mantlet pocket collects a lot of water, since there is no way to drain it.
- The sloped lower sides of the fighting compartment make it harder to store ammunition. It is reasonable to make them vertical.
- The headlight should be put on a flexible mount, since the existing headlight was shattered by the shockwave from firing.
- The commander's station is comfortable. His position, unlike on the SU-152, is along the axis of movement of the SPG. The commander has the ability to comfortably observe the battlefield and the SPG's movement due to his rotating hatch.
- The driver's station has advantages over that of the SU-152 in terms of accessibility and working conditions.
- The gunner's station is comfortable and much better than in the SU-152 in terms of working with the aiming mechanism, trigger mechanism, and sights.
- The loader's station is roomy, but the loader can only use ammunition from the racks along the left side of the vehicle. It is easy for the loader to take rounds (12 units) from these racks and load them. The rest of the ammunition (one to the left of the driver, 7 under the gun breech) are hard to retrieve.
- The breech operator's station is rather cramped by the breech and side of the hull, especially when the breech is to the far right. The breech operator hands the loader propellant charges from the right side of the hull. It is tight, but possible to extract the 16 casings along the right side of the vehicle. It is not possible to extract the 4 charges stored under the gun breech in combat conditions.
It is possible to calibrate the sight.
- The overall drop in muzzle velocity after 309 rounds, 244 of which were supercharged, is 0.8%, which is normal for this caliber. The wear on the barrel is normal.
- The absence of a muzzle brake, in addition to simplifying production, makes observation of the target after firing easier.
- The work of the recoil brake is satisfactory. The function of the recoil speed and return speed is normal. At φ=10 the recoil resistance is 6% less than calculated, which is explained by a proportion of the energy of the recoil being absorbed by the SPG itself.
The recoil length is stable within 850+/-40 mm.
Recoil length tends to be around the maximum side and is explained by an installation of a spindle produced at lower end of tolerances due to finishing at factory #172 and installation of an experimental adjustment ring, which gave extra long recoil at factory #172 trials compared to the stock adjustment ring with a narrow ribbon.
- The sight offset is negligible.
- No deformation or unexpected wear was noticed during measurement of components and assemblies of the system.
- The system worked without fault. Occasional failures to extract are caused by casings that were reused many times (as many as 10).
- The design of the fighting compartment, armour, and crew work stations have significant advantages over the stations in the stock SU-152 SPG."