In addition to some 600 articles published in more than 30 periodicals, Būčys published a number of separate books on various topics. He published a collection of his articles as separate books "Tikėjimo dalykai" in 1913 and "Gyvenimo pagrindas" in 1931. His most important work is a three-volume theological work aimed at an average priest and school graduate. The three volumes on God the Creator, Jesus Christ, and the Holy Spirit were published in 1929–1932. His popular works include books about the Lourdes apparitions (first published in 1909, third edition in 1943), cautionary tales promoting the temperance movement (in 1925 and 1939), parents' right and obligation to raise and educate their children (in 1927), a conversation about the soul (in 1930). He also published guides for priests (collection of sermons in 1936, spiritual exercises in 1925), theology textbooks (brief apologetics in 1922, 1923, and 1926, on fundamental theology in 1923 and 1926, on theological encyclopedia in 1925), historical and demographic study on the Eastern Orthodox and Old Believers in Lithuania (in 1936), an essay on education arguing that the state should only finance schools that should be run by communities and organizations in 1918, a report on the 29th Eucharistic congress in 1929, a review of a book on ethics by Adomas Jakštas ("Su Jakštu per pikto laukus" in 1937), a work of fiction ("Rapukus kaupiant" in 1928), and others. He wrote six notebooks (396 pages) worth of memoirs and published excerpts in "Tėvynės sargas"; they were published posthumously in 1966. He left other thick volumes of manuscripts on his thoughts for the Marian Fathers, on good behavior, and miracles of Jesus as well as an extensive biography of Justinas Pranaitis.