Ballistic Energy

Predicted speed

282.8 fps

74.0 ft-lb · 0.523 slug-ft/s

Target margin

+9.0 ft-lb

Against the 65.0 ft-lb goal

Required speed

265.0 fps

Needed for 416.7 gr at the current energy goal

Test arrow

416.7 gr

27.00 g · 29.0 in · 14.37 gr/in

1. Start With What You Measured

Measured profiles

Each tab is one real arrow build with one real chrono result.

Profile name

27.00 g 29.0 in 14.37 gr/in 6.04 gpp

Measured let-off

Draw weight 69.0 lb

Draw length 27.5 in

Arrow length 29.0 in

Finished arrow 416.7 gr

27.00 g · 14.37 gr/in

Chrono speed 278.8 fps

2. Enter The Build You Want To Test

Test build

This is the setup you are considering right now.

27.00 g 29.0 in 14.37 gr/in 6.04 gpp

Test let-off

Draw weight 69.0 lb

Draw length 27.5 in

Arrow length 29.0 in

Finished arrow 416.7 gr

27.00 g · 14.37 gr/in

Energy goal 65.0 ft-lb

Tools

Converter and quick utilities

Use this when you want to translate grains to grams or check gr/in fast.

Finished arrow weight Arrow length Grams

27.00 g 29.0 in 14.37 gr/in

Status

Measured profiles auto-save locally. Export JSON whenever you want a portable snapshot.

3. Read The Answer

Decision readout

Best projected result is pinned at the top, then the full comparison table follows.

Best current profile

Arrow 1 +9.0 ft-lb margin

282.8 fps · 74.0 ft-lb · 27.00 g measured arrow

Profile	Measured	Test result	KE	Margin
	278.8 fps 71.9 ft-lb	282.8 fps +4.0 fps from measured	74.0 ft-lb 0.523 momentum	+9.0 ft-lb

How speed changes as finished arrow weight changes

This isolates finished arrow weight while keeping the chosen draw weight, draw length, and let-off fixed.

Y · fps X · grains

Energy across likely arrow weights

The dashed line is the energy goal. Profiles above it clear the target at that weight.

Y · ft-lb X · grains

Field manual and equations Detailed notation, exact equations, the fitted speed model, and how to read the comparison charts.

Exact ballistic equations

These equations are fixed. If mass and speed are known, energy and momentum come directly from the formulas below.

Kinetic energy

KE = grains × fps² 450240

Velocity is squared, so small FPS changes can move KE sharply.

Momentum

p = grains × fps 225400

Momentum scales linearly with both mass and speed.

Required speed

fps_required = √ ( target KE × 450240 grains )

For the current test build, the threshold is 265.0 fps.

Fitted speed model

Each profile is a measured anchor. The model starts from that measured chrono result and then moves away from it using tunable sensitivities.

fps_estimate = fps_measured + Δdraw weight × (fps per lb) + Δdraw length × (fps per inch) - Δarrow grains / 5 × (fps lost per 5 grains) + Δlet-off bonus + bias trim

Measured profile

The stored combination of draw weight, draw length, arrow length, arrow weight, let-off, and chrono speed.

gr/in

Finished arrow grains divided by finished arrow length. This helps compare density across builds.

gpp

Finished arrow grains divided by draw weight. This is still shown because many hunters use it as a floor check.

Advanced settings

Model sensitivities and chart range live there so the main page stays focused on normal decision work.

How to use the page

The page is intentionally split into the common user path: enter measured data, enter the test build, then read the projected answer.

Measured profiles are your trusted anchor points.
Test build is the setup you are considering changing to.
Decision readout sorts profiles by target margin so the most useful answer rises to the top.
Charts show how speed and energy move if finished arrow weight changes around your selected range.
Converter lets you move between grains, grams, arrow length, and overall gr/in quickly.