Expresso, Murphy's Law rules in AS scenarios and HD incidents,as in all human endeavour. but the chance of a perp clearing a jam I can't seems rather slim.
And while the HD 870 here has a mag extension, reality insists that more than one shot/perp is a scant possibility,and barely worth preparing for.
However, having been on the wrong end of long odds before, I'll grab a backup sidearm as indicated. The More Is Better Principle is oft correct in these things...