Following what several forum members mentioned over the years for every 10 grains over one would lose an average of three feet per second.
When Edgetac started advertising the 775 grain arrow point, I was using that as my speed calculation as up until then I had not physically shot
that arrow-point weight combination. Edgetac proved my calculation wrong and suggested the accurate way was to shoot through a chronograph.
I then built some arrows to try to achieve his 775 grain point weight plus my 325 grain average arrow shaft which would average around 1100 grain
Just reweighing and shooting these arrows prior to this write up, here is what I am showing shooting through a chronograph one arrow length from
the front of the stirrup. My arrow measurements are including the point from the center of the 1/2 moon nock. The crossbow I used today is a Center
Point Sniper XT390 with the complete riser from a Center Point Heat 415. Two shots were taken using the same arrow each time.
1) 21" Blood Sport Witness with point 427.8 grain total. Two shots 380, 379 feet per second.
2)22 1/4" Carbon Express Pile Driver modified 1112 grain total. Two shots 249, 248 feet per second.
3) 21 1/4" Blood Sport Witness modified 1105 grain total. Two shots 249, 249 feet per second.
If one used the formula for every 10 grains over losing 3 feet per second, one will see the huge difference when shooting through the chronograph using
heavier arrow-point weight combinations.
A) Arrow #2 = 1112 grain - Arrow #1 = 427.8 grain = 684.2 divide by 10 = 68.4 x 3 = 205 feet per second loss which would have showed 380 - 205 = 175
feet per second. The chrono graphed speeds were 249, 248 feet per second.
B) Arrow # 3 = 1105 grain - Arrow #1 = 427.8 grain = 677.2 divide by 10 = 67.7 x 3 = 203 feet per second loss which would have showed 380 - 203 = 177
feet per second. The chrono graphed speeds were 249, 249 feet per second.
Thanks to Edgetac for the helping me achieve the proper speed calculation.