I wrote a very long post addressing this and other matters, which you can find here. To give you the highlight more relevent to your specific question:

All of this isn’t to say that it didn’t happen at all, but only that those limited instances paled in comparison not only to overall casualties, but also when compared to the fate of the vast majority of soldiery who ended up on the wrong end of Soviet discipline, and thus that the extent of blatant machine-gunning imagined by many ought to be considered essentially mythic^24 . Even excluding the reduction in role of the Red Army’s blocking units after 1942, by far, the most likely outcome of punishment under Order 227 would be placement within the previously mentioned penal unit, or the gulags, as opposed to execution, let alone a Maxim to the back. Although numbers are incredibly hard to be certain of, Overy cites 442,000 men sentenced to penal units, and 436,000 imprisoned. Through the entire war, 158,000 were sentenced to execution as according to Krivosheev^25 , some 13,000 or so alone during Stalingrad^26 .

24 Reese, Why Stalin's Soldiers Fought, 175

25 Overy, 160

26 Christian Hartmann, Operation Barbarossa: Nazi Germany's War in the East, 1941-1945 (Oxford: Oxford University Press, 2013), 127 Keep in mind that that is for all offenses, not just those guilty under Order 227.