We've seen the idea of mounting an A-19 gun on a SU-152 before, but the plan was never actually implemented. Here is another iteration, with a little more reasoning.
"To the member of the Military Council of Armoured and Mechanized Forces of the Red Army, Lieutenant-General of the Tank Forces, comrade Biryukov
I report my ideas on the topic of armament of the SU-152 (on the KV chassis). The existing SU-152 SPG has one drawback along with many of its positive qualities, specifically that the ML-20 152 mm gun is basically a howitzer. As a result, when shooting at long ranges, on the order of 2000 meters, the angle of elevation is high and the target is no longer within the field of view of the sight.
Along with the 152 mm ML-20 gun, NKV factories produce the 122 mm A-19 gun, whose oscillating part is identical to the ML-20's. The A-19's shell has a flat trajectory, and the penetration of the gun is greater than that of any other gun used by the Red Army.
I think that it is reasonable and necessary to arm half of produced SU-152s with 122 mm guns. This will allow the SPGs to freely combat any existing enemy armoured vehicles at long ranges.
No design changes are necessary. All that must be done is the 152 mm barrel should be exchanged for a 122 mm one and new 122 mm ammunition racks should be installed.
I ask you to support my request to the director of the Kirov factory to produce one prototype of a SU-152 with a 122 mm A-19 gun. This SPG must undergo gunnery trials and the results of the trials will decide whether or not the tanks will be re-armed. The Kirov factory already has A-19 guns.
Chief of the GBTU Tank Directorate, Engineer-Colonel Afonin
Deputy Chief of the 6th Department of the Tank Directorate, Engineer-Major Voroshilov"
CAMD RF 38-11355-1401