Wolverine, I'm shooting these arrows out of my 70# bows only. They are .350 spine arrows. By swapping from a 43 gr. insert to a 90 will definitely weaken the spine. That's why I was asking about a 75 grain head. Currently shooting 100 gr. heads with the 43 gr. inserts. On Victory's chart, that's nearing a weak spine, but still safe. Switching to a 90 gr. insert and a 75 gr. head still is adding another 22 gr. to the front of the arrow, which is enough to weaken the spine. Front end weight weakens a spine, rear end weight strengthens a spine. Picked up some 75 gr. FP's today, so I'll give them a try and see how they work out with the new inserts.