While poking around at Soviet Gun Archives (a very cool site which I wish was updated more often), I noticed this two-page memo reporting the results of an experiment modifying SVT-40 rifles to full-auto capability.
To put this into context, the original SVT-38 was updated based on combat experience in Finland, and the SVT-40 formally adopted on April 13, 1940. Although the rifles had some problems (field reports described them as unreliable and inaccurate in combat conditions), they were successful enough that Tokarev went on to design a select-fire variation. The changes were mostly in the trigger group, with the safety lever turned into a selector switch allowing either semi or full-auto fire. The intention was that the rifles could be used in full-auto in limited circumstances to supplement the Soviet shortage of light machine guns and submachine guns. Designated the AVT-40, these rifles went into production in May 1942 – and were taken right back out of production in the summer of 1943.
Mechanically, the SVT-40 was simply not equipped to withstand the rigors of full-auto fire. It suffered from parts breakages, as well as failures to eject, premature unlocking of the bolt, and ruptured case heads. In addition, it was found to be less accurate that the Mosin-Nagant in semiauto and less accurate than the PPSH-4 and PPS-43 in full auto. These problems are detailed in the 2-page report above. Here is a translation, again from Soviet Gun Archives (I have emphasized a couple points that jumped out at me in particular):
Conclusions on the proving ground trials of 7.62 mm automatic rifles, converted from semi-automatic rifles, with 10-15 round magazines showed that:
- Groups at 100 meters when firing in bursts increase by 3-3.5 times.
At 300 meters, only 25-30% of the bullets strike a 3×3 meter target.
At 500 meters, up to 30% of the bullets strike a 3.5-4 meter target.
While shooting with a 15 round magazine, grouping gets worse, and it is difficult to fire while prone due to the protruding magazine.
- When shooting at targets, only the first bullet hits.
- The ability to aim is limited to 50 shots over the span of one minute. After that, the barrel overheats, and a mirage effect is achieved, which impedes aiming.
- The automatic rifle jams:
- With thick grease: 2-4% of the time
- With dry parts: 12-14%
- In dusty conditions: 14-50%
- While aiming up or down: 8-12%
- The barrel life is 6000 rounds when firing 50 rounds per minute, after which the rifle was allowed to cool. Continuous fire brings the life down to 150-200 rounds.As a result of trials, it was concluded that:
- Is is not viable to create an automatic rifle from a semi-automatic one by modifying the trigger group.
- It is only possible to aim with such an automatic rifle when using a thickened barrel and lightened bipod.
- When converting a semi-automatic rifle to fully automatic by only modifying the trigger group, its combat usefulness decreases to less than that of a submachine gun.Conclusions
- Due to the decreased combat usefulness, conversion of a semi-automatic rifle to a fully automatic one is not rational.
- In order to reach required density of fire with a high probability of hitting the target, it is better to use submachineguns, which have the advantages of simpler production, higher reliability, compactness, high magazine capacity, larger stocks of ammunition, etc.
The US military would discover this ineffectiveness of full-auto shoulder rifles about 15 years later, with the M14 debacle…