V3X speed question

[Hunter24]

Hey all. I have a Mathews V3X and am trying to set it up with a heavier (to me) arrow. It’s the V3X 33, 29in draw, 85% mod. In the shop it shot 298fps with a 403grain arrow. When I got it home I have 27 3/4 C2C hunter xt arrows 300 spine that I added 50grain insert weights to for a taw of 475. I chronoed 5 arrows that were consistently 287-288. A bit later I shot the same 5 arrows on the same chrono at 276-278. Is it normal for a chrono to do this? Which groups speed seems to be the more accurate of the two?

Sorry for the newbie question and lack of posts. I’m looking to change both of those things

 

[Mighty Mouse]

A bow's kinetic energy output remains roughly constant across arrow weights. Assuming your shop-recorded speed/weight numbers are accurate, you can calculate baseline KE: (Arrow Weight in gr) × (Arrow Speed in fps)² ÷ 450,240 = 79.5 ft-lbs. Using that baseline KE to solve for speed at 475 gr yields 275 fps. So I would say your second set of speeds chrono'd at home is more accurate.

I have seen wide variations in chrono'd speeds depending on lighting conditions (indoor vs. outdoor, sunny vs. shady).

 

[MT257]

Was chronograph inside or outside?

 

[406unltd]

My 33 chrono speed was 278 and 280. My dl is 30.5, arrow is 530g, poundage is 71.5.

 

[Billy Goat]

I'm going to guess the second set of numbers are the accurate ones, tho normally it's easier to get slower numbers than faster. Lighting plays into optical chronos, but so does angle. You need to make sure you shoot flat across the sensors. Shooting 5" over the front, then 4" over that back sensor makes the arrow take a longer path than 4.5" and 4.5", thus slowing the reading.

Now if it's @ 75# id believe the upper 80's numbers and think you weren't flat over the sensors, but I don't see a 33 hitting upper 80's with 70# and the numbers you gave.

 

[Hunter24]

Thanks for the all the advice. The chrono was outside in full Colorado sun for the first group and partly cloudy for the second. The fact that the shots within each group had such a small consistent spread was what kind of threw me for a loop.

 

[wayoh22]

V3X 33, 30in DL, 75lbs, TAW = 421grains coming in at 316FPS

 

[Tahoe1305]

Fwiw, I’m shooting a V3X 29” with about the same weight arrow (465g) and 75#/85% DL 27” and getting 285fps. So with the 2” longer draw length and 70# mods I’d believe the 285+ numbers.

I’m betting lighting could be the cause. Using the IR light kits may help.

 

[hartigjosh]

v3x 33 with 30 in draw and the shop got mine cranked to 78.5 lbs. I have those rip tko arrows with 50 plus 125 tip. I was shooting right at 290 fps in the shop when I checked. I have not weighed my arrows, but this should give you an idea.

 

[hartigjosh]

Anybody using a spott hogg and if so what tape number did you use when calibrating?

 

[Hunter24]

I’m gonna fool around more with my chrono this weekend and maybe take it to the shop to compare readings. I guess the chrono I have is probably not the best quality. Also I plan on picking up a fast Eddie xl so maybe the sight tape will provide some insight. FWIW I’m using a fixed pin sight now. It was surprisingly and noticeably slower by adding 50gr inserts. I guess it’s a more significant weight increase than I thought

 

[Tahoe1305]

I’m gonna fool around more with my chrono this weekend and maybe take it to the shop to compare readings. I guess the chrono I have is probably not the best quality. Also I plan on picking up a fast Eddie xl so maybe the sight tape will provide some insight. FWIW I’m using a fixed pin sight now. It was surprisingly and noticeably slower by adding 50gr inserts. I guess it’s a more significant weight increase than I thought

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archerycalculator.com

Lots of calculators online. Can see the exact effect on weight vs speed.

That calc says 75g increase was going to cost about 25fps.

 

[Ho5tile1]

My V3X 29 at 28.5 77.6 pounds slings my 550 grain arrows 277 fps when I had it on 29 inches it was 283 fps so seems reasonable


Sent from my iPhone using Tapatalk

 

[Hunter24]

FWIW my sight tape is 280.5. I had to make a custom sight tape because past 70ish yards my holds did not match up