The volume 9 of "Kurogane no Linebarrels
" DVD includes an extra episode "Tensai Bishoujo Kagakusha Rachel-chan Episode 1". The DVD will be released on August 26th. "Rachel-chan" manga has been published in Champion RED Ichigo as a side story of Linebarrels manga.
Another extra episode of Linebarrels, presumably episode 2 of Rachel-chan, will be provided for those who complete all the volumes of the DVD.
Source: Linebarrels Official Website