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Object 261 Assault gun

The self-propelled artillery installation "Object 261" was developed in the KB Chelyabinsk and Leningrad Kirov factories on the basis of an experimental heavy tank IS-7. The engine used was a modified diesel M-50 high power set. The light-armored open wheelhouse housed a powerful 152-mm M-31 cannon, developed at the design bureau of the Perm plant No. 172 based on the ballistics of the Br-2 cannon and was unified in some parts with the M-51 tank gun. The gun M-31 was tested in October 1948. The project of self-propelled artillery installation "object 261" was developed in 1947.

Despite the failures with the previous high-powered power-assisted self-propelled guns, the idea of putting super-power cannons on self-propelled chassis did not leave the Soviet leadership after the war.

The deeply modernized gun BR-2 received a new name - M-31. The modernization was carried out so deeply that little remained of BR-2. Design work was carried out by the design bureau of plant number 172. The main differences from BR-2 were as follows: not a piston, but a horizontal wedge semi-automatic shutter, a powerful slit muzzle brake that absorbed up to 70% of the recoil energy. The barrel of the gun was supplied with a massive breech to obtain the required weight of the sliding parts and to better balance the swinging part. The loading of the new gun was separate-sleeve.

Loading the projectile was made with the help of spring rammer, cocked automatically during rollback. The mechanism for blowing the barrel bore worked the same way automatically. It used compressed air from a separate cylinder. The rollback brake was made hydraulic, and the knurled pneumatic. Two cylinders brake recoil and two cylinders knurled made rigidly connected with the barrel. Thus, due to the breech and recoil devices, the weight of the rolling pieces was significantly increased, which, together with the muzzle brake, gave a very small recoil for a gun with such ballistics (520-mm against 1400-mm for the Br-2).

The lifting and turning mechanisms of the gun were of a sector type with a worm self-braking link. The lifting mechanism had only a manual drive, since the GAU electric drive requirement was removed (a rather strange decision). The M-31 gun had a TP-47A sight for direct aiming and a ZIS-3 sight for firing from closed positions. And finally, this gun was originally designed unified with a 152-mm tank gun M-51, which had the same ballistic data.

The technical design of the M-31 cannon, finalized and coordinated with the Chelyabinsk plant, was sent for review and conclusion to the Artcom GAU at the end of 1947. The gun turned out just unique data. The firing range of the gun was almost 28 km (27,800 meters) with an initial projectile speed of 880 m / s. However, the project of the 715 project submitted by the Chelyabinsk plant (later it became known as the IS-7 tank) was not approved, and it was returned to the plant for revision. In this regard, a radical revision of the entire gun layout was required, although there were no significant comments when considering its technical design.

Considering the first design experience, Plant No. 172 was asked to coordinate the gun project with the ACS project based on the IS-7 tank (Ob. 261), developed in Leningrad. This work was carried out by plant No. 172, and on August 23, 1948, the revised design of the M-31 cannon was submitted to the GAU for consideration, as applied to the combat detachment of the SAU on the basis of IS-7. However, the project and this ACS (object 261) was also rejected.

Again, NTK BT proposed the Leningrad Kirov Plant to redo the layout of the entire self-propelled gun. Plant No. 172 again had to change the design of the cannon, or rather, its machine, as the swinging parts of the cannon never changed. By the way, speaking of this, it can be concluded how close IS-7 was to the conveyor. On the basis of experienced unapproved chassis, our designers did not develop ACS. But let's touch on a bit the project itself ACS as a whole, as I said above, it was to be produced on the chassis of the IS-7. It should have been fitted with a modified ship diesel M-50 with a power of 1050 hp. (same as on IP-7). With such a motor, according to the designers, the ACS had to reach a speed of 55 km / h and had a cruising range of 300 km. As for the ammunition, then in the project SAU it has not yet been approved.

The gun and the calculation should have been placed in the lightly armored open wheelhouse. This suggests that the designers of this SAU did not plan its participation in tank duels. But the SAU base was left well armored (apparently for the sake of unification with the IS-7) and it had armor from 215 to 150 mm. It is not difficult to guess, with such data self-propelled turned out to be more than heavy. The weight was supposed to be somewhere around 68 tons. True, and her donor IS-7, the mass was approximately the same.

It should also be noted that the alteration of the chassis of the IS-7 tank was assumed to be rather deep. The ACS was supposed to be based on, as it were, back to front of the deployed chassis. That is, the engine and drive wheel, should have been located in front of the self-propelled gun.

This ACS also did not see the light even in an experienced performance. After the decision was made to abandon the production of the IS-7, this project, of course, was also rejected.