The article examines one of the sections of the Russian orthoepic system that has undergone a major change over the past hundred years – the pronunciation of vowel letters o and а in the 1st pre-stressed syllable after [ш, ж, ц]. The position under consideration was initially contradictory: the consonants [ш, ж, ц] were previously soft, then they hardened, but the vowels after them continued to behave as if they were positioned after the soft ones. In the first third of the twentieth century, the norm was established, according to which in the vast majority of cases, in the position of the 1st pre-stressed syllable after [ш, ж, ц], in accordance with the stressed [o] – [ыэ] is pronounced, and in accordance with the stressed [a] – [аә]. However, in the modern norm there are a few deviations from this rule. The results of the experimental study largely contradict the lexicographic recommendations. In the words with o, this letter can be pronounced as [ыэ], [э], [аә], [о], but their distribution differs for specific words and is determined by a set of different factors: 1) the presence of conditions for inter-syllabic assimilation of vowels (жокей, шоссе), 2) the unstressed sound [o] allows you to either emphasize the "alienness" of the borrowed word (креп-жоржет, шокировать), or the infrequency of the vocabulary (жонкиль, шортгорн), or highlight the word in a strong prosodic position. In the words with a, this letter could be pronounced [ыэ] и [аә] are fixed. At the same time, it can be stated that most words with the norm under consideration have already "survived" the stage of orthoepic variation and are pronounced as a general rule with the sound [аә] (жара, шаги, цари), and in other words, the ratio of variants inherent in the previous orthoepic section has been ‘preserved’. There is no evidence at the moment that the process of replacing the variant [ыэ] with the variant [аә] in these words continues.