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.
Not happy with our calculations or how it works? Let us know.
Have a suggestion for a calculator you don't see here? Let us know.