I think the ammo partly was my fault I meant "inferno shells" (DH core book page 143 / RT core book page 137)
and at least for inferno shells you can do a normal full burst with your shotgun and depending on your rule itnerpretation the target must make 1 AG test or 1 AG test per hit and is set on fire if he fails... no primitive no single shot only... of course this works with bolter weapons as well
and shotgun > bolter is true as long as the house rules from op are used and the situation is point blank but only because (and this is wanted if I read correctly) shotgun+point blank > everything else