Technically there's four small clips on each select-fire bolter...
www.games-workshop.com/MEDIA_CustomProductCatalog/m1183520_99110101367_BitzDeathwatchConversionMain_873x627.jpg
www.games-workshop.com/MEDIA_CustomProductCatalog/m1183515_99110101367_BitzDeathwatchConversion1_873x627.jpg
Unless they pass clear through the bolter, which would seem wierd.