Barrel-Length Velocity Loss (Estimate)
Rough rule-of-thumb estimate of velocity change from cutting or extending a barrel.
How this works
Powder keeps burning and accelerating the bullet the entire time it's in the barrel, so a shorter barrel gives the powder gas less distance to push before the bullet exits — and a longer one gives it more. This calculator applies a straight-line fps-per-inch rate to that length difference, which is the same simplified approach most published gunsmith rules of thumb use.
Where published rates actually come from
Real velocity-loss-per-inch figures published by barrel makers and reloading manuals range roughly from 10 to 40+ fps per inch depending on the cartridge, and the relationship isn't perfectly linear — the last few inches of a very short barrel typically cost more velocity than the last few inches of a long one. Treat this as a planning estimate before a barrel job, not a substitute for chronographing the actual result.
Frequently asked questions
How many fps do I actually lose per inch of barrel cut?
It varies a lot by cartridge — published rates commonly range from about 10 to 40+ fps per inch depending on the powder and case capacity involved. The default in this calculator is a rough middle-ground estimate, not a fixed constant.
Is the relationship perfectly linear?
Not quite — the last few inches of a very short barrel typically cost more velocity than the last few inches of a longer one, so this straight-line estimate is most reliable for modest length changes.
Should I chronograph before and after a barrel job?
Yes, if possible — this calculator is a planning estimate for deciding whether a barrel change is worth it, but the only way to know your actual velocity change is to chronograph the same load before and after.
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