Butterfly with PFS

skarrd said:

long draw [behind ear lobe]

Click to expand...

"Long short draw"- I hadn't heard it put this way before, but I like it! And I have been pondering this over the past week. So apologies for the long post with a lot of "thinking out loud", but you shook the tree I have been climbing all week.

While playing with fork width and all recently I have been comparing my cheek anchor to my under the ear lobe anchor. As the "long short draw" aptly captures, my under the earlobe anchor is a good inch and a half longer than my in front of the ear lined up with my cheek bone. And just this morning I had the chrony out and figured out that this makes a 2-3% difference. Not much, but something. And real and reproducible.

The other difference is that the in front of the ear or on the cheek bone is higher and closer to the line of sight, which means less hold under / over at reasonable ranges, but faster drop off at longer ranges. All relative to line of sight- the actual trajectory doesn't really change. The lower behind the earlobe anchor has does have a bit more hold under / over at closer ranges, but relative to line of sight stays above the target longer (launched at a steeper up angle relative to line of sight).

So I dove into a black powder round ball ballistics program that was put up here (I can't remember who posted it) and have been driving myself crazy trying to decide if I want to shoot a wider fork from behind my ear lobe or a narrower one from a higher anchor / with a shorter draw.

In the end I decided to make identical frames and try both ways, with the fork width adjusted to have the frame dead on for vertical at ~15 yards for each anchor. If the playing around with the ballistics program is right, even 3/8" ammo going at 240 fps (entirely reasonable) should be maximum 2" over or under at any range between 5 and 20 yards. And 5/16" stays within 1.5" over or under anywhere from 5-20 yds when going 265 fps.

Now to see about matching reality to theory. Personally I'm rooting for the "long short draw" as I like this anchor and although the difference is small, it does produce a bit more power.

And once I get it all figured out to my satisfaction, I will probably scrap it all and go full butterfuly full time.