In retrospect, it’s remarkable how much faith the US had in its soldiers’ abilities to control a full-power automatic weapon. The answer to the question “is a full-caliber automatic infantry rifle a good idea” was well within reach by even the early forties, as this Soviet document on testing of the avtomat variant (AVT-40, pictured at the bottom of the title image) of the SVT-40 proves. From the translation:

Conclusions on the proving ground trials of 7.62 mm automatic rifles, converted from semi-automatic rifles, with 10-15 round magazines showed that:

1. 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.
2. When shooting at targets, only the first bullet hits.
3. 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.
4. The automatic rifle jams:
   1. With thick grease: 2-4% of the time
   2. With dry parts: 12-14%
   3. In dusty conditions: 14-50%
   4. While aiming up or down: 8-12%
5. 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:

1. Is is not viable to create an automatic rifle from a semi-automatic one by modifying the trigger group.
2. It is only possible to aim with such an automatic rifle when using a thickened barrel and lightened bipod.
3. 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 submachinegun.

Conclusions

1. Due to the decreased combat usefulness, conversion of a semi-automatic rifle to a fully automatic one is not rational.
2. 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.”

Indeed! The US was experimenting with automatic rifles in full-power rifle cartridges during the same time, but despite this held firm to the idea that this kind of weapon heralded the future of US small arms. Perhaps their love affair with the full-power squad automatic rifle blinded them to what should have become obvious in testing? Obviously once fielded, this wishful thinking quickly evaporated.

H/T, the imitable Ensign Expendable, of Soviet Gun Archives and Archive Awareness blogs.