hi kerry -
a while back i looked at the versa pack at the local gunshop and thought that the bore on one of the barrels looked off-center, that is, when i looked at the barrel from the breech end.
i can't recall which barrel caught my attention or if i was simply having having a premature senior moment.
if my recollection is right, that may be why standard barrels do not fit the versa pack receiver, as the firing pin may not be in the center of standard barrels.
sg