I was reading one of Bernie Pellerite books today (IDIOT PROOF ARCHERY)and he's saying its not the energy that results in penetration, its the efficient use of energy that does. One of his examples was two difrent arrows shot from same 60 lb. bow one was 307 grain carbon flying 282 fps.and the other was 567 grain aluminem arrow flying 218fps.
567 arrow 60 lbs kenetic energy one foot behind chrono
307arrow 54 lbs kenetic energy one foot behind chrono
same test now but taking measurement 20 yards from chrono=
307 arrow 50.5 lb
567 arrow 52 lb
again same test at 29 yards both arrows produced nearly same amount of kenetic energy307 =269 f.p.s. 49.34 foot pounds and the567 grain arrow at 198 f.p.s.=49.36 foot pounds
so at 30 yards the light arrow would actualy carry more energy!