In terms of the present article the features of the unstressed vocalism after unpalatalized consonants are described in the Bryansk dialect of early 17th century. This analysis is based on two manuscripts: Bryansk and Karachev otkaznaya kniga. Local business documents are the important source of linguistic information to reconstruct the phonetic system of dialects of the Russian language, because they reflect real dialectal features. In the present paper the author makes an attempt to describe the vocal system of the first pretonic syllable, which is characterized by a specific type of the vowel reduction, which is called zhyzdrinskoje dissimilative akanje, spread in the West Russian area. An attempt to highlight the individual features of pronunciation of the scribes, based on the local business documents is made. In the article the language material of the second pretonic syllable is analysed and the specificity of vowel neutralization in the post-stressed final open and closed syllables and in the post-stressed non-final syllables is describe.