I know this isn't an exact science, but approx. how much additional Axis/Beman 500 arrow length would I need to allow a reduction in point weight of 75 grains?
Bow design and orientation of the shelf meaning whether its cut past,dead on,or an eighth off center will have lote to do with that.I get a 1/2 inch per 25 grains.I'd guess within 1 and 1/4" to 1 1/2",but your best option is to put it to the test bareshafting.I've discovered that putting HIT inserts in with hotmelt really isn't hard.You may have to reheat the very tip of the shaft briefly to get it seated all the way,but it will allow you pull the insert if need be.
Hope this helps,
Ethan