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Soviet sights for machine guns and light machine guns: PSO-1U

Originally by user “akinfo (Pavel P)” on gunsforum.com, but in Russian so who knows if this info will disappear soon. Saved here in English for posterity.

In the second half of the 70s, the Central Research Institute No. 3 of the Moscow Region carried out research work “Investigation of the possibility of increasing the efficiency of firing 5.45-mm machine guns”. 
Work under the code “Potpourri” was approved by the Commander-in-Chief of the Ground Forces in 1975. 
The purpose of the work was to develop the main tactical and technical requirements for a new 5.45 mm assault rifle, which provides an increase in firing efficiency up to 1.5 times compared to the standard 5.45 mm AK74 assault rifle.
When substantiating the basic tactical and technical requirements for samples of small arms, a model of combat between a Soviet army unit and an enemy grouping was used, when both belligerents have the same type of weapons. 
In this model of a battle between two groups, a motorized rifle company of the Soviet Army armed with AK74 assault rifles and a US infantry company armed with M16A1 automatic rifles were considered. 
It is assumed that all combat units are reconnoitered before the start of the battle and that an equal number of combat units participate in all types of combat operations on both sides.
As a result, the following results were obtained:
Analyzing the influence of three main factors: the numerical strength of combat units, their combat rate of fire and the probability of being hit by a burst on the result of the battle of groups armed with AK74 and M16A1, it was concluded that the initial numerical strength of combat units has the most decisive influence on the outcome of the battle, and two other factors influence weaker and more or less equal. 
With equal initial strengths of full-time combat units of the MCP SA, with a slight margin, wins the oncoming battle, reliably wins in a defensive battle, but loses in the offensive to an enemy infantry company with M16A1 rifles.

To increase the likelihood, various measures were developed and evaluated, one of which concerned the use of optical sights on machine guns.
Conducted platoon tactical exercises with live firing showed that when attacking the front line of the enemy’s defense, submachine gunners fire 2-3 bursts per minute and 1-2 bursts per minute when fighting in depth. 
It is assumed that putting a four-fold optical sight on the machine reduces aiming errors and reduces the dispersion of bullets of the first rounds of bursts to 1.5 thousandths when firing on the move from a short stop, that firing through an optical sight does not change the combat rate of fire.If, however, setting up an optical sight will reduce the combat rate of fire from 0.22 to 0.17 bursts per minute, then the results of the battle are improved in favor of the MCP up to 20% (taking into account only the reduction in aiming error). 
With an increase in the effective combat rate of fire from 0.22 to 0.32 rounds / min, together with the installation of an optical sight, the results of offensive combat can be improved in the interests of the MCP SA at ranges up to 100-500 m up to 2 times.

If in a defensive battle (shooting from an AK74 assault rifle is carried out from a prone position from an emphasis on target No. 6), AK74 assault rifles have four-fold optical sights, then the loss indicators in comparison with a regular AK74 assault rifle without an optical sight improve at ranges of 200-600 meters in 1 .5 times, and at ranges up to 100 m – 1.01 times.
Conducting research took several years, as a result, one of the main conclusions of Potpourri was the need to equip Kalashnikov assault rifles and light machine guns of the rifle department with small-range sights, not only optical ones, but also collimator ones.
            All the leading design bureaus of the country of the Soviets began to develop (or borrow) optical and collimator sights for AK74N assault rifles and advanced models.
            In this article, I want to talk a little about the sample known as: unified sniper optical sight, PSO-1U index.
 
PSO-1U
            Since 1977, the Izhmash Production Association of the Ministry of Defense Industry (hereinafter referred to as Izhmash) has been one of the manufacturers of PSO-1 sights, which were equipped with SVD rifles produced by Izhmash.
            As part of the development of various research and development projects that appeared by the end of the 70s, since 1979 Izhmash began to develop a modification of the PSO-1 sight – a sight named as PSO-1U (nified), because. 
as conceived by the author of a private technical assignment, TsNIITOCHMASH, the sight should have been designed for installation on a line of weapons for the rifle squad: AK74N, AKS74N, RPK74N, RPKS74N, SVD. 
Already in 1981, prototype sights of optical sights PSO-1U and PS-4 were presented for in-plant tests at Izhmash,
The purpose of the test was to determine the durability and reliability of prototype PSO-1U and PS-4 sights, to identify the possibility of installing these sights on AK74N assault rifles and SVD rifles.
The PSO-1U sight was developed on the basis of the PSO-1 optical sight and differed from the latter in the body layout, micro-tumbler placement, hidden reticle illumination wiring, SM-2.5 lamp mount, clamping mechanism and mounting bracket. 
The aiming line has been raised by 5 mm compared to the PSO-1.
Fig.2 General view of the PSO-1 sight on the AK74N assault rifle (from the test report)
Fig. 2 sight PSO-1U
Fig.3 and Fig. 
4 sights PS-4 sight
These changes provided at that time:
Installation of the sight on products AK74N, AKS74N, RPK74N, RPKS74N, SVD and other samples that have an installation base in accordance with the requirements of GOST B 18.972-73.
Increasing the level of unification with the PGO-7V sight, from which the mounting bracket with a clamping mechanism and individual parts of the reticle illumination system were completely borrowed.
Reducing the complexity of manufacturing by eliminating a number of parts required in the existing design for attaching external wires and sealing them, as well as by simplifying the design of the housing, protecting the microtumbler, mounting the lamp and reducing the range of parts and assembly units due to unification with the PGO-7V sight for RPG-7 hand grenade launcher, also produced at Izhmash.
Improving the tightness, improving the appearance of the sight and the convenience of controlling the toggle switch of the MT-1 microswitch.
The possibility of using a short mounting base on the SVD rifle according to GOST B 18.972-73, which increased the manufacturability of the base.
The ability to remove the SVD receiver cover with the sight installed and the exclusion of a caliber to control the gap between the light bulb and the receiver cover.
The possibility of a better view when aiming at an open sight with an optical sight installed in the event of a sudden failure of the optical sight.
The PS-4 sight was a modification of the PSO-1U sight and differed from it in greater simplicity, reliability and tightness due to the exclusion of the screen assembly.
Before firing tests, the sights PSO-1U (No. 2 and No. 5) and PS-4 (No. 8 and No. 9) passed acceptance tests in accordance with AL3.812.000 TU (TU for PSO-1 sights) in full and passed them without comments.
 
Determination of accuracy of fire
At the beginning of the tests, the accuracy of fire of AK74N assault rifles with PSO-1U and PS-4 devices and without devices was determined.
A single fire test was carried out at a distance of 100 m and 300 m. The accuracy of firing with automatic fire from AK74N assault rifles was determined from various positions: from the position “lying from the stop under the fore-end” to a distance of 100 m, from the position “lying with a hand” and “standing with hands” at a distance of 25 m. Tests for each sample were carried out by shooters of various qualifications. 
For each case, 3 series of 20 shots were carried out. 
In the tables below, I will give the average data for 3 series.
One of the comments to the PSO-1U was that the experimental design of the body and bracket on the PSO-1U and PS-4 devices did not ensure the installation of devices on the SVD rifle due to rubbing against the receiver cover. 
As it was installed at the shooting range – free mounting of the sight and smooth movement along the guides is possible only after changing the dimensions of the body and bracket. 
In these first tests, the mounting of the sights was provided after the locksmith processing of the brackets and housings.
Accuracy of shooting at a distance of 100 m with a single fire.
It follows from the data in the Table that the PSO-1 optical sight at a distance of 100 m, on average, gave an improvement in the accuracy of fire by 1.12 ± 1.38 times in comparison with an open sight.
Accuracy of fire at a distance of 300 m with a single fire.
It follows from the data in the Table that the PSO-1 optical sight at a distance of 300 m, on average, gave an improvement in the accuracy of fire by 1.25 ± 1.54 times in comparison with an open sight.
Accuracy of fire with automatic fire.
It can be seen that when firing automatic fire from the AK74N from the “lying down from the stop under the forearm” position at a distance of 100 m, the PSO-1U optical sight worsens the accuracy characteristics. 
Particularly significant (up to 12.5 cm in these tests) is the deterioration of lateral scattering. 
When analyzing the results, it was noticed that, in addition, a significant shift of the midpoint of impact (STP) was revealed when firing from the AK74N with automatic fire from the PSO-1U (up to 19 cm to the left and up to 30 cm up during these tests). 
All the shooters noted the inconvenience of aiming and the inconvenience of holding the AK74N when firing automatic fire with an optical sight: the location of the sight was inconvenient in height and length.
 
 
Tests with a large number of shots
Tests with a large number of shots were carried out in accordance with TU MO No. A8769-78 letter O2 for the AK74 assault rifle. 
When cooled with water through the barrel bore, the optical sight was separated from the sample. 
During the test, the accuracy of shooting with a single fire at a distance of 100 m was determined by a qualified shooter (Lebedev). 
The results of checking the accuracy of fire are given in the Table:
According to the accuracy of fire at the beginning and during the tests, the PSO-1U met the requirements of TU MO No. A8769-78. 
15120 shots were fired from the AK74N assault rifle with PSO-1.
After 10000 shots with sights, 2500 shots were fired at a temperature of +50ºС and 2500 shots at a temperature of -50ºС.
It was noted that the fastening of the devices on the machine guns during the tests was reliable, there was no spontaneous withdrawal of the fastening handle during firing. 
There were no comments on the appearance of the sights and the optical system.
 
Determination of overloads acting on the PSO-1U sight when firing from AK74N
The g-forces were measured using a KD-13 piezoelectric g-force sensor and an IPU-5(2) impact parameter meter when firing from the shoulder on an AK74N No. 132004 assault rifle.
The sensor was mounted on the sight alignment mechanism.
The results are shown in the Table:
Service durability
Additionally, for a more complete assessment of the strength characteristics of the sights and the efficiency of use on the AK74N assault rifle, after testing with a large number of shots, the PSO-1U No. 2 sight was tested for service strength by falling with the AK74N assault rifle in the following sequence:
 
Falling on the sand
There are no comments on the appearance of the sight, the operation of the mechanisms and the optical system after the falls.
When checking after falling on the collimator, no knocking down of the aiming line was found.
Fall onto a concrete pad covered with 15 mm thick felt
After five falls from a height of 1 m from a horizontal position onto the left side of the machine (the left side of the sight), the protective shield of the backlight microswitch toggle switch was crushed and the handle AL8.333.295 was bent. 
Switching the toggle switch is possible. 
The bend of the cam handle did not interfere with the attachment of the sight.
After 12 falls on the butt from a height of 1.5, a destruction (stratification) of the battery was found.
After 3 falls from a height of 1 m to the top of the sight, the aiming line was knocked down by acceptable values ​​- 0-01 up and 0-01 to the left.
For all other types of fall, the aiming line knockdown was no more than 0-00.25, which met the requirements of the specifications for PSO-1. 
There were no comments on the mechanisms and optical system.
 
Fall on a concrete pad
Five falls were made on the buttstock from a height of 1.5 m. After the first fall, the sight separated from the machine gun without leaving the handle (due to deformation of the cam).
After the second and third falls, the sight shifted back along the guides by 3 mm without leaving the handle. 
After the fourth fall, the displacement was 5 mm; after the fifth, it was 10 mm. 
After each fall, the sight was placed in its original (working) position.
Additional tests
Due to the breakage of the wall of the bracket stop and the spontaneous withdrawal of the handle during testing with a large number of shots from the SVD, the bracket was finalized with a durability test when tested with a large number of shots from the SVD.
The sight with a modified bracket design and increased hardness of the PSO.006 handle was tested by drops from an AK74N stock onto a stock from a height of 1.5 m onto a concrete base. 
Made 6 drops. 
There was no displacement of the sight from the mounting base, however, with each fall, the handle broke off the latch.
 
Test Conclusions
An experimental optical sight PSO-1U (No. 2) was tested up to 15120 shots with an AK74N assault rifle. 
The mounting of the sights during the test was reliable, there was no spontaneous withdrawal of the bracket handle during the tests. 
The scopes have sufficient durability.

The use of the PSO-1U sight improves the accuracy of firing from machine guns with a single fire at a distance of 100 m by an average of 21 ± 38% and at a distance of 300 m by an average of 25 ± 54%.
The location of the sight on the machine is inconvenient for conducting aimed fire in bursts. 
With automatic fire from the position “lying from the stop under the forearm” at a distance of 100 m, the characteristics of the accuracy of fire deteriorate, especially in lateral dispersion (up to 12.5 cm) and the average point of impact is significantly shifted to the left (up to 19 cm) and up (up to 30 cm ).

The PSO-1U sight (No. 2) showed sufficient service strength when falling from AK74N onto sand and a concrete pad covered with felt.
The sight PSO-1U (No. 5) was tested up to 9000 shots with the SVD rifle. 
During the tests, spontaneous withdrawal of the handle occurred.

The handle has no locking mechanisms in the working position. 
After 3000 shots, numerous drops of lubricant were found over the entire area of ​​the sight reticle.

The sight provided the required TU MO No. A7930-70 lit. 
A (TU on SVD) accuracy of fire both at the beginning of the test and after 6000 shots.

The brackets, modified in the direction of increasing strength and improving the reliability of fastening, passed durability tests of up to 6000 shots with SVD rifles. 
The latch securely holds the handle in working position when firing.

The handle with increased hardness ensured a reliable mounting of the sight on the AK74N assault rifle when falling onto the stock from a height of 1.5 m onto a concrete base.
Conclusion
PSO-1U and PS-4 sights, tested with AK74N assault rifles, showed sufficient reliability, durability and improved dispersion characteristics by single fire and can be recommended for operation on AK74N when firing with single fire. 
Before mass production, testing of bodies made of cast billets is necessary.

It is necessary to improve the convenience of aiming when firing from AK74N with automatic fire and increasing the hardness of the handle material (AL8.333.295) for a more reliable fixation of the sight on the machine.
For reliable mounting of the sight on the SVD rifle, it is necessary to fix the handle in the working position, as well as increase the strength of the support surface of the bracket.
There is no need to increase the length of the threaded part of the bracket for the AL8.919.115 screw.
 
Further development
            Throughout the first half of the 80s, the PSO-1U sight was tested and compared with other experimental sights that competing enterprises of the Ministry of Defense Industry presented for research.
But the Secret Decision of the GRAU MO VS USSR and the Ministry of Military Industry of the USSR in 1985 approved the design documentation of the letter O1 for the sight. 
As the text of the decision stated:
Based on the PSO-1 sniper optical sight, the Izhmash enterprise developed design documentation for the PSO-1U unified sniper optical sight. 
The prototypes passed factory tests in 1980-1983. 
and testing at the Rzhev test site
 19th Research Order of the October Revolution Red Banner Order of the Patriotic War test site – approx. 
author 
) in 1984. The samples passed all the tests.
The purpose of the work carried out was to introduce changes into the design of the PSO-1 sight that improve the characteristics of the sight and achieve the possibility of its use on other types of small arms.
The result of the work was the creation of a unified sniper optical sight PSO-1U, which differs from the PSO-1 sight in the following characteristics:
Increased reliability of the grid illumination system due to open sealed wiring.
A higher degree of unification with a serial optical grenade launcher sight PGO-7V (from RPG-7).
The ability to install and use the sight on AK74N, AKS74N assault rifles, RPK74N, RPKS74N, PKMN machine guns by changing the design of the sight mounting bracket, introducing interchangeable scales for the aiming angle mechanism and raising the optical axis of the sight by 5 mm.
The performance characteristics remained the same as on the PSO-1.
The decision read:
Conclusion 573 VP MO on review of design documentation to approve.
Approve the design documentation for the manufacture and acceptance of a unified sniper optical sight as documentation of the letter O1 for mass production.
Operational documentation is allowed for use in the troops and for the acquisition of the first serial products.
The product, its full name is considered unclassified.
In this case, the conclusion of the 573 military representative office of the customer was used to review the design documentation for the PSO-1U unified sniper optical sight.
Rice. 
5 Decision 573 VP
When considering the design documentation in VP 573, it was found that the design documentation was completely corrected based on the results of manufacturing an experimental batch. 
The changes made to the documentation did not affect the performance characteristics of the product. 
Changes are verified in production and are protected by tests in the scope of periodic. 
There were no comments on the results of field tests.
The design of the product provided a fairly high level of standardization and unification. 
About 67% of the parts were borrowed from the PSO-1 and PGO-7V products. 
Test methods and measuring equipment for the PSO-1U product are unified with PSO-1. 
Maintainability is maintained as in PSO-1.
In accordance with the Additional Agreement, Izhmash manufactured, and the 573rd military mission accepted and shipped an experimental batch of 200 PSO-1U sights. 
The accepted products comply with the requirements of the design documentation. 
The documentation is suitable for series production.
The PSO-1U sight does not use materials and components that are not allowed for use in special equipment, scarce.
Rice. 
6 Sight PSO-1U as standard
Rice. 
7 Delivery set of the PSO-1U sight in standard version with scales for different types of weapons
Rice. 
8 Serial sight PSO-1U in a case
   As you can see in the Figure, the serial versions of the PSO-1U also received a bracket fixation mechanism that prevents spontaneous separation of the sight and a set of interchangeable correction scales for all types of small arms of the compartment.
Rice. 
9 Sight PSO-1U No. 00015 from the collection of the Museum. 
M.T.Kalashnikova
        Unfortunately, the results of firing with the main type of fire from machine guns and light machine guns, namely automatic (bursts) with a PSO-1U sight, were inferior in efficiency to an open sight. 
It was this that served as the stop factor, due to which the USSR Ministry of Defense never accepted the product into service, limiting itself to trial operation in the troops, and Izhmash, in the conditions of the impending economic crisis, did not develop the PSO-1U for hunting carbines and on this story PSO-1U can be said to be over.
            At the end of the article, I would like to brag not as an author who opens unknown pages in the history of Kalashnikov weapons, but also as a collector of Kalashnikov weapons and accessories.
            In 1986, the AP-4N optical sight mounted on AK74 assault rifles was tested in comparison with the PSO-1U sight.
The AP-4N sight, designed and manufactured by Izhmash on the basis of the optical scheme of the PSO-1U sight and intended for installation on AK74N assault rifles, received a metal rear sight illuminated by a tritium light element instead of a glass mesh, which made it possible to exclude a number of details of the PSO-1U illumination system. 
The tritium light element was made in the form of a glass ampoule and can operate at a temperature of ±50ºС without replacement for 10-15 years. 
In order to simplify the operation and the alignment mechanism, the side handwheel is excluded. 
To simplify the design, the mounting bracket (seat) is made together with the body of high-strength aluminum alloy AL2CHP.
The most surprising thing is that the PSO-1U sight took part in the tests, the first in a series from 1984 under the number No. 001. 
This scope is currently in my collection.
Rice. 
10 Mention of the sight PSO-1U No. 001 in the test report
Rice. 
11 and Fig. 12 sight PSO-1U from the collection of the author of the article
Operational and technical characteristics of sights AP-4N and PSO-1U
The test conclusions regarding the PSO-1U sight did not say anything new in general, the PSO-1U, AP-4N optical sights improve the accuracy characteristics of the machine gun when firing a single fire compared to an open sight:
Rice. 
13 test report PSO-1U No. 001
But in comparison with an open sight, the characteristics of the accuracy of the AK74 assault rifle worsen when conducting automatic fire from the “lying from the stop”, “standing from the hand” positions by about 20-30%.
The reason for the deterioration of the characteristics of the accuracy of fire during automatic fire are:
Difficulty finding a target.
The shooter’s head is not pressed with his cheek to the butt of the machine gun, “hangs in the air.”
The characteristics of the accuracy of fire of the AK47 assault rifle with the AP-4N sight are worse than with the PSO-1 sight by an average of 8-10% from all positions, with the exception of the “lying down” position with a single fire at a distance of 100m with a poorly lit target due to a clearly visible metal rear sight, providing more convenient and faster targeting.
 
Author:
Pavel P., ak-info, 2021

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