Soviet high caliber smoothbore gun usage in the 1970's

In the 1970s, UKBTM conducted experiments with high calibre rifled guns, primarily using 130mm designs as their main focus. At the time, the Soviet Union standardized their 125mm 2A26 guns. 

The idea was put in motion in the year 1970 by S.A. Zverev who at the time was the head of the Ministry of Defense and Industry. According to a document issued in 1970, the first three Object 172Ms were to be equipped with three different guns: a standard 125mm 2A26, a 130mm rifled gun with a hydraulic lifting mechanism made by Uralmashzavod or a 130mm rifled gun with mechanical lifting mechanism, designed by the Perm Machine-Building Plant. 

However, in October of 1970, the order for 130mm guns was cancelled for unspecified reasons. 

3 years later in 1973, designers returned to the idea, after a mockup of a tank with a 130mm LP-28 rifled gun was created. 

• Ability to quickly change the barrel without having to remove the entire gun assembly from the tank (first time in the USSR) 
• Ability to fire guided munition 
• Improved accuracy 
• Increased barrel thickness closest to the breach
• The symmetrical arrangement of recoil dampeners on the breach (first time in the USSR)
• Presence of a thermal sleeve on the barrel 

The gun successfully passed the debugging and acceptance tests by firing and was installed on the experimental tank "product 172MN" (N - rifled), developed in the UKBTM on the basis of the Object 172M. The development of the 130-mm rifled tank gun 2A50 (LP-36E) as part of the tank was carried out from 1973 to 1975. During the work, two prototype T-72 tanks with LP-36E "Object 172MN" were manufactured.

In addition to the advantages, the disadvantages of the gun also became obvious: a larger gun and its ammunition increased the weight of the tank and made it difficult to assemble the combat compartment. But the main thing is that the gun did not have modern ammunition. The work on them was slowed down by the head of the GRAU, Marshal of Artillery P. N. Kuleshov. He was an ardent supporter of smoothbore artillery and was uncompromising in his views.

And although in June 1975 both experimental tanks Object 172MN with 2A50 (LP-36E) were sent to Kubinka for testing, and the new Object 172-3M, was also equipped with 2A50 (LP-36E), which was manufactured at the turn of 1975-1976, had no prospects. 

As a result, tanks with a 130-mm rifled tank gun 2A50 (LP-36E) were not accepted into service. 

In the later years, another 130mm gun was created using LP-36E but instead of being rifled it was designed to be a smoothbore variant. 

Vehicles used for testing: 

1. Object 172MN (1973-1975)
2. Object 172-3M (1976)

Taken from: S.V. Ustyantsev, D.G. Kolmakov. UKBTM. 75 years of the Tagil tank building school, 2017