Naval Historywith Dr. Alex

Q&A · 4:04:28-4:05:36

Why a longer gun barrel can increase muzzle velocity

Propellant pressure falls as a shell moves down the barrel, but a longer barrel gives the expanding gas more time and distance to transfer energy before the projectile exits.

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Question

Why do longer gun barrels produce higher muzzle velocity if expanding gas loses pressure as the shell travels down the bore?

Short answer

Because the gas acts on the shell for longer, transferring more total energy even while its pressure gradually falls.

Notes

The question correctly identifies that expanding propellant gas loses pressure as volume behind the shell increases. Declining pressure can still continue accelerating the projectile. A longer barrel keeps the shell under useful pressure for more time and distance, allowing additional energy transfer before it reaches the muzzle. Muzzle velocity rises when that extra impulse outweighs friction and other losses, even though the instantaneous gas pressure is no longer at its peak.