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Load development

Seating Depth Calculator

Translate your measured distance to the lands into a target COAL, magazine fit check, and seating depth guidance.

Cartridge overall length at which this exact bullet first contacts the rifling lands. Measure for your chamber and bullet lot.

From your comparator or seating depth tool. Use inches.

Distance the bullet travels before contacting the rifling. Enter a positive value to seat away from the lands.

Positive values move off the lands; zero equals jam.

Longest cartridge overall length that feeds freely from the magazine, allowing practical clearance.

Optional. Adds a fit check for AR-15, AICS, or pistol mags.

Measured base-to-tip length of the bullet. Paired with case length to estimate how deeply the bullet is seated.

Optional. Enables seating depth calculation when paired with case length.

Actual length of a prepared case from case head to mouth. Use a representative measured value from this batch.

Optional. Use trimmed length for the brass you are loading.

Target COALCalculated cartridge overall length from case head to bullet tip after subtracting the desired jump. —
Jump from landsPlanned free-travel distance between the seated bullet and the rifling lands. —
Seating depthEstimated length of bullet held inside the case: case length plus bullet length minus target COAL. —
Magazine marginMagazine length limit minus target COAL. A positive value indicates estimated clearance. —

Application

Notes and checks

Use these metrics to set your seating die and confirm field fit.

  • Enter your measurements to generate notes.