? about calculating KE and TRUE FPS
03-23-2004, 05:00 AM
#11
Boone & Crockett
Join Date: Feb 2003
Location: Lehigh County PA USA
Posts: 12,157
RE: ? about calculating KE and TRUE FPS
heres another question ive never shot carbons so i have no clue, will a carbon at for example 390gr finished shoot faster than an aluminum at 390gr finished?
03-23-2004, 05:08 AM
#12
Nontypical Buck
Join Date: Feb 2003
Location: Arlington TX USA
Posts: 2,214
RE: ? about calculating KE and TRUE FPS
ORIGINAL: JoshKeller
I'll also take a stab at it..
IBO speed is 308.
308 - 10 fps for the ultra nok (aluminum is heavier than a string loop, and makes more noise)
298 fps. - 8 - 10 fps for the kisser and peep.
288 fps. - 5 fps for the whiskers.
283 fps
I, too, will assume xx78's and that you use the uni bushing.
I came up with a 534 grain arrow with 7.4% FOC.
I've generally found that 5 grains = 1 fps.
534 - 350 (ibo) = 184/5 = 37 fps.
283 - 37 = 246 - 250 fps, for a total of approx 70 - 73 ft lbs of KE.
Id estimate the AMO speed of this bow at 230 - 235 fps. Added your 10 lbs of draw weight, I think this is fairly close. I think you'd gain approx 10 fps by loosing the ultranok.
I'll also take a stab at it..
IBO speed is 308.
308 - 10 fps for the ultra nok (aluminum is heavier than a string loop, and makes more noise)
298 fps. - 8 - 10 fps for the kisser and peep.
288 fps. - 5 fps for the whiskers.
283 fps
I, too, will assume xx78's and that you use the uni bushing.
I came up with a 534 grain arrow with 7.4% FOC.
I've generally found that 5 grains = 1 fps.
534 - 350 (ibo) = 184/5 = 37 fps.
283 - 37 = 246 - 250 fps, for a total of approx 70 - 73 ft lbs of KE.
Id estimate the AMO speed of this bow at 230 - 235 fps. Added your 10 lbs of draw weight, I think this is fairly close. I think you'd gain approx 10 fps by loosing the ultranok.
29" arrow length x 11.67 gpi = 338 grains for arrow shaft only
I used 16 grains for the insert
I used 13 gains for the nock
I used (3) 4" vanes for 27 grains
I used 10 grains for the uni bushing
I used 100 grains for the field tip/broadhead
I come up with a total arrow weight of 504 grains.
For speed deductions:
-4 fps for peep sight.
-6 fps for Ultra Nock (figured about the same deduction as 2 brass nocks)
-6 fps for the whiskers.
-3 fps for the kisser.
I come up with 238 fps based on an IBO rating of 308fps.
03-23-2004, 05:53 AM
#13
Join Date: Feb 2003
Location: SC USA
Posts: 1,434
RE: ? about calculating KE and TRUE FPS
Mike is very close with the accessories IMO........I don't know what the arrow weight is for a 2315 !
I have chrono'd a loss of 6 fps for an Ultra nock and maybe 1 fps with a string loop (and they don't hurt nearly as bad if you clip your arm
) ! I have gotten a 2 fps loss on two different kisser buttons !
WV , My Outback is hitting around 272-274 on 70# 30" draw with 450 grain Axis 340's , with a WB rest , string loop , and a tru peep !
I generally see a 1 fps loss for every 3 grains with any of my last 4 Mathews ! So I would guess(like Mike) at about 240-245 fps for a 504 grain arrow with your accessories !
I'm currently shooting mine maxed on 75# and getting 282-285 fps w/ the Axis' (80 #KE
) !
I just didn't think string silencers made a difference so there's an extra 5 fps IMO !! And you can pick up a tremendous amount of speed with an arrow change..........my PSE CF arrows @ 350 grains shoot 298 fps on 69 # out of the Outback with a WB rest .......303 fps with a prong rest ! So the skies the limit.......however I am liking the heavier arrows and the trajectory difference between 300 fps and 280fps has been so minimal ......it's not worth mentioning !!
I have chrono'd a loss of 6 fps for an Ultra nock and maybe 1 fps with a string loop (and they don't hurt nearly as bad if you clip your arm
) ! I have gotten a 2 fps loss on two different kisser buttons ! WV , My Outback is hitting around 272-274 on 70# 30" draw with 450 grain Axis 340's , with a WB rest , string loop , and a tru peep !
I generally see a 1 fps loss for every 3 grains with any of my last 4 Mathews ! So I would guess(like Mike) at about 240-245 fps for a 504 grain arrow with your accessories !
I'm currently shooting mine maxed on 75# and getting 282-285 fps w/ the Axis' (80 #KE
) ! I just didn't think string silencers made a difference so there's an extra 5 fps IMO !! And you can pick up a tremendous amount of speed with an arrow change..........my PSE CF arrows @ 350 grains shoot 298 fps on 69 # out of the Outback with a WB rest .......303 fps with a prong rest ! So the skies the limit.......however I am liking the heavier arrows and the trajectory difference between 300 fps and 280fps has been so minimal ......it's not worth mentioning !!
03-25-2004, 12:47 AM
#14
Nontypical Buck
Join Date: Feb 2003
Location: Martinsburg, WV
Posts: 3,215
RE: ? about calculating KE and TRUE FPS
Mike, I plugged in the xx78 2315's in www.bowjackson.com It came out with 534. On the serious side, my dad had one of those ultranoks screws come out, and shot an arrow about 30 feet in the air. He bought another, and had the thing break and smacked himself in the nose pretty good. He was loosing 9 fps with one of those things too.
