The 5-grains-per-pound floor (vertical bow)
The 5-grains-per-pound floor (vertical bow): what it is and how it changes the arrow you should shoot.
Dry-fire warning
Crossbow bolt data and archery arrow spine, nock and thread data are quoted from each manufacturer's published figures, owner documentation and industry standards, cited on every page. A nock, spine or grain-weight mismatch can cause a dry-fire that damages the bow and can injure the shooter. Confirm against your own owner's manual and the arrow maker's own chart before shooting, and never drop below the stated minimum total weight.
| The rule | At least 5 grains of total arrow weight per pound of draw weight |
|---|---|
| 70 lb example | A 70 lb compound needs a minimum 350 grain arrow including the point |
| Why | A too-light arrow leaves excess energy in the bow, like a partial dry-fire, and can damage limbs or cams |
| Crossbow parallel | The same 5-grains-per-pound floor sets the minimum bolt weight on the crossbow side |
Field notes
The 5-grains-per-pound rule is the weight floor that sits alongside spine. Multiply draw weight by five and that is the lightest total arrow weight, point included, the bow should shoot.
A 70-pound compound therefore wants at least a 350-grain arrow. Going lighter to chase speed leaves energy in the limbs and cams instead of the arrow, which is the vertical-bow version of a dry-fire.
This is the same floor BoltFitFinder applies to crossbow bolts, where the minimum total grain weight protects the limbs the same way.
Related rules and examples
Sources: Easton Archery - Target and Hunting Arrow Selector · Nock On Archery - Arrow Spine Chart: choosing the correct spine