I think it has to do in most cases with the broadhead being on the ferrule or taper correctly.
I put on broadheads and then spin test them; point down arrow straight up and spin; if there is a wobble of the shaft where it is attached to the broadhead; the arrow will fly badly.
If your using aluminum shafts or carbon; and using screw in broadheads- or if you use aluminum inserts you may never notice this wobble; or bad flight.
But if you test your arrows for broadhead alignment and see a wobble; fix it and the arrow will fly much better- to perfection.
At one point (
) factory broadheads were coming out rapidly - new heads all the time; and very often they were not balanced at all. I had some razorback 5s that all were unbalanced to where the arrows went everywhere but where I wanted.
Then too; if you use a straight fletch- your incouraging the chance of broadheads flying where ever they want. A good helical fletch can overcome some unbalanced broadhead problems- the less the twist the greater the chances the broadhead will effect flight if its unbalanced.
With wood shafts the problem of the broadhead not being balanced is much greater; and every broadhead mounted on a shaft should be spun to make sure its on straight.
Tapers can be off a little; glue can be thicker on one part of the broadhead than another- and it can cause unbalanced broadhead placement and bad broadhead flight.
I always put hot melt on and then the broadhead and turn the broadhead on the taper to even the glue.
If you have never had a bad broadhead take over your arrow your lucky- or just plain good at making arrows
I won't even enter into spine and bow weight stuff that might effect flight.
I think people know if they practice with a 125 grain field point; and shoot a 160 grain broadhead things will be a little different..