The balance point remains in the exact same spot if the broadhead weighs the same as the field tip. I've actually found the balance point and marked it with a felt pen and when switching to a broadhead, had it balance on the same mark - repeatedly.
When you measure to the back of the insert and totally disregard what's going on out in front, as long as the weight doesn't change the balance point doesn't change. For setting up broadhead arrows though, I far prefer the old fashioned method that measures the total length of the arrow, from nock to tip. With that method, the balance point does shift, and it shifts in the wrong direction.
Your point about only being able to tune to your shooting ability is a good one. However, I don't quite understand tuning to group size. I've never seen anyone measure their groups. How would one know if at one adjustment point, group size was 3.125" or 3.375"? It would take painstaking measurements that would unlikely be very accurate.
You've obviously never shot field archery.Background... It'sa game of accuracy and consistency, shooting 4-arrow groups atevery target (though afew stations have multiple targets with one or twoarrows each)from about 10 feet to 80 yards.There is no slop factor allowed like you get in 3D. You know the exact distance to the target. You shoot four times which means you might get lucky on one or two shots, but not four in a row. You shoot 112 arrows in a round instead of just 30 or 40 which puts a huge demand on consistency. The smaller and more consistentyour group sizes, the better your score...as long as your groups are centered in the target. [&:]
When you're shooting groups at 60 yards - the distance I set for my longest pin - small tweaks can make dramatic differences in group sizes. When you've gotten the bow tuned to give you the smallest groups you can get at 60, that correlates to smaller group sizes at the shorter distances as well.
I've never, ever, had a bow fine tuned in that wayfor shooting field points that would shoot broadheads to the same point of aim. I've never seen ANYBODY that did, and I was fortunate enough to belong to a club that counted some of the best archers in Texas among it's members. Those were guys I made a point to hang out with and they taught me a great deal about shooting and tuning.
At the time, we also had unknown distance broadhead shoots (set uplike 3D but using fiberboard cutouts with piles of clean sand for backstops). The broadhead shoot was usually an add-on at the end of a standard field shoot, and we were required to use the same bow for both. So, I - along with every other person I shot with - had a dovetail sight mount and two sets of sights - one sighted in for field points and the other sighted for broadheads.
I remain unconvinced that impact will be significantly different on a setup that is correct. I'm referring not only to the bow's tune, but arrow spine, FOC, spine matched arrows and tuned broadheads. Maybe it has something to do with how I tune everything. I use stiffer than normal arrows, lots of helical feathers, very high FOC, heavier than average arrows
It has EVERTHING to do with how you tune. If you tune specifically to get your field points and broadheads to strike the same POI, what else can you expect when you tune to meet that specific goal?
Different goals require slightly different tunes. For field archery, my goal was to get the very best accuracy and consistency with field points. I got that, but my broadheads refused to strike the same POI. When I tuned specifically for broadheads using the same method,field points did not strike the same POI. I could have tuned to get both to strike together, but I would have remained at NFAA class B instead of being able to play with the Big Boys in A class. (I don't think NFAA uses the class breakdowns any more due to low participation.It's a shame more people don't do field archery, because they'dbecome much better shooters if they did.)
If you think that getting bare shaft/field points/broadheads all striking together is a good thing, set that as your goal and wind up with good enough accuracyto serve your purposes, then tuning the bow to get them all together is a good thing. Just remain aware that the bow is slightly DETUNED from shooting either oneperfectly.
Joe, you are correct that shooting a release instead of fingers diminishes the variation. It doesn't eliminate it though.