Yeah i could see how the shrapnel theory would apply as weak as brass is (for metals); otherwise, the casing itself will project the bullet 'on a path.' and i'm sure it sort of still did, but far weaker; no defect or deformity upon stiking something (hard) probably...
did the guy get struck by case fragments? or by actually forgetting where his arm was? who's to say...let's give him SOME credit as a man who tests his own half-assed theories...right after we call him !!!STUPID!!!