View Full Version : BP Rifle Velocity

January 23, 2009, 09:48 PM

I came across an article In "Invention & Technology" magazine dealing with the "Kentucky Rifle". The author stated that "Davy Crockett occasaionally increased the velocity of his .40 caliber flintlock to a remarkable 2500 FPS by loading it with six fingers of gunpowder." (Wonder what kind of chronograph he had!)
The only BP I shoot is percussion revolver, so I don't know anythig about what a rifle is capable of. But 2500 FPS seems like kind of a stretch. This FPS sounds to me more like BS! :D

Double J
January 23, 2009, 10:07 PM
The .32 and .36 can do even better than that. Closer to 2600 FPS. But the ball doesn't like speeds much over 2000. They tend to get erratic in flight.
The .36 with a 117 grain Maxi will get to 2400 and shoots straight. This makes for a versatile little rifle. Load light and have .22 short power, or load up to near .30-30 power for coyotes.
Seems that .40 or a .44 is about the breaking point as far as velocity goes.
Some of the .40's are quit accurate.

January 24, 2009, 12:16 AM
Most of the BP rifles I have fired turn out about 1,500 fps, maybe 1,800 fps, but that's about all BP can do. Cap and ball or cartridge guns are better at it than flintlocks because of better gas sealing. After all, the flame front on BP only travels at about 2,500 fps IIRC, so any more is out of the question.

January 24, 2009, 12:46 AM
Dunno but I get almost 1900fps out of my .54 Lyman Great Plains Rifle with patched roundball. Superbly accurate.

January 24, 2009, 02:03 PM
My Flintlock rifle with a 32 inch barrel 45 cal. with 90 grs GoexFF goes
2,000 fps on a chrony. The old rule of thumb was to use the same powder
charge as the ball weights for 2500 fps.

January 24, 2009, 05:58 PM
Mass is conserved in a chemical reaction and that means that the gasses that propel a projectile out of a gun weigh just as much as the gunpowder that turned into gasses.
As posted earlier, at around 2500 FPS, the gunpowder charge starts to weigh just as much as the bullet and that means that it takes just as much energy to accelerate the gasses as it does the bullet. At higher velocities, the gasses outweigh the bullet and there is a limit where accelerating the gasses generated by the gunpowder consumes all the energy of the powder explosion.

This is also true of smokeless powder cartridges, the smokeless powder charge of a .220 swift or .22-250 comes close to the same weight as the bullet and it's hard to shoot bullets faster than that without ridiculous increases in pressure and barrel life measured in dozens of shots.

NASA built a research high speed gun to simulate meteor impacts on spacecraft. Instead of using powder to generate gasses, an explosive charge was used to compress hydrogen (the lightest known gas) to drive a pellet down a three story tall barrel to a velocity of about 30,000 FPS. At those velocities, air in the barrel acts like a barrel obstruction so the gun shot into a vacuum.

January 24, 2009, 07:10 PM
Well, I learned something today! :D Thank you!
I never would have thought that BP rifles would go much over 2000 FPS.
I get around 1050 with 40 grains of Pyrodex and a conical bullet in my Old Army.