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What arrow spine for 55 lb draw at a 28 inch arrow

The starting spine for a 55 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 55 lb draw at a 28 inch arrow with a 100 grain point, start with a 400 spine (the 340-400 band), and keep the finished arrow at or above 275 grains total.
This setupmanufacturer data, cited
Draw weight55 lb
Arrow length28 in (cut, nock groove to shaft end)
Point weight100 gr
Recommended spine400 (published band 340-400)
Minimum total weight275 gr, from the 5-grains-per-pound floor
A shaft in this spine

Field notes

A 55 lb draw at a 28 inch arrow sits in the middle of the 340 to 400 band and lands on 400 with a standard 100 grain point. It is a common women's and youth-adult hunting spine.

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 55 pounds, or bare-shaft test before cutting a dozen.

Whatever spine you land on, keep the finished arrow at or above 275 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