BoltFitFinder
Arrow spine by setup · bolt datasheet

What arrow spine for 50 lb draw at a 28 inch arrow

The starting spine for a 50 lb draw at a 28 inch arrow with a 100 grain point, and the weight floor.

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.

For a 50 lb draw at a 28 inch arrow with a 100 grain point, start with a 500 spine (the 400-500 band), and keep the finished arrow at or above 250 grains total.
This setupmanufacturer data, cited
Draw weight50 lb
Arrow length28 in (cut, nock groove to shaft end)
Point weight100 gr
Recommended spine500 (published band 400-500)
Minimum total weight250 gr, from the 5-grains-per-pound floor
A shaft in this spine

Field notes

A 50 lb bow flexes the shaft less, so it drops out of the 340 to 400 band into a 500 with a short 28 inch arrow and a 100 grain point. A longer arrow would move it back toward 400.

Spine is a starting point, not a guarantee, because a 340 from one brand can differ from another. Confirm on your arrow maker's chart at 28 inches and 50 pounds, or bare-shaft test before cutting a dozen.

Whatever spine you land on, keep the finished arrow at or above 250 grains total, the 5-grains-per-pound floor, so the bow is not shooting dangerously light.

The rules behind this pick

Sources: Nock On Archery - Arrow Spine Chart: choosing the correct spine · Sportsman's Warehouse - Arrow Spine Charts: Compound, Recurve and Traditional