Something has to be jamming the auger, or something is binding on them. I've sucked in some small 2x4 pieces in the past and only blow the fan shear pin, never have broken an auger pin (yet - knock on wood). I've also sucked in some bigger rocks and blown the fan pin (and bent one fan blade), but no effect on the augers.
Check the clearances around the augers in regard to the housing. See if the auger is hitting somewhere. If one of the auger "screws" is bent out of shape, it may be hitting the gear housing (fragile die-cast metal) or some other part of the housing.