One footnote about the Soviets and recoilless guns was that they were able to build them for their armed Almaz space stations (and the failed Polyus 'Death Star' which @AndyC has written about), which is rather important as firing a gun with recoil will potentially knock your space station out of orbit.
Wouldn't really change that much, IMO. Most of their prewar stocks, whatever the quality, are going to get walloped in 1941 no matter what. And that's assuming production isn't stopped and shifted to an easier and simpler alternative even before the war once the problems develop, which leaves a few hundred guns at most which are then used up in the early war.