To the best of my knowledge the majority of todays bows are warrantied for arrows of 350grains. I personaly shoot around 365 grains and I dont think my bow is going to blow up tomorrow as DavidMil stated. Now granted you will get a little more vibration and hand shock out of a 365 grain arrow compared to that whopper of a arrow he shoots, but with the high quality bows and vibration dampening devices they have today its pretty much a minimal difference. As for Straightarrow's comment about KE and being all over the chart for Dr. Ashby's test. Im pretty sure regardless of arrow weight, KE, Speed pretty much anything the results on live animals is going to be all over the place. It all dependds on where you hit them, and further more I never said KE determines penetration, read my post a little more carefuly.