Originally posted by Mike Bolin: I am guessing it is because most broadheads are at least slighty.....and in alot of cases, quite a bit longer than a field point. But that is just a guess. An inch longer arrow shaft changes spine quite a bit. If you shoot a longer broadhead, ie. woodsmans, tuffheads, grizzlys ect. it could be an inch or more longer than your field point. Good guess?