where does velocity top out?

[Jkwas]

I understand that when you go from a 4in barrel to a 2in barrel you lose about 100fps, but where does velocity top out? If you go from a 4in barrel to a 6in barrel, do you pick up an extra 100fps? For example, in a 38spl revolver.

 

[griz]

A 22 rimfire is about the mildest cartridge avalible, and it tops out around 18-24 inches depending on which one is used. The big rifle rounds are still gaining velocity at any practical barrel length. (well over three feet anyway) The 38 special would be in between. My guess would be somewhere around three feet, again depending on the round you pick.

 

[MrAcheson]

It depends on the cartridge and cartridge design (powder volume, burn rate, etc.) I've heard some .22s top out by 16". 9mm is supposed to start running out of steam by normal rifle lengths as well because of the small case and fast powder that is normally used.

On the other hand magnum pistol calibers are still gaining speed at sane rifle lengths, although not the 50 fps/inch that is generally used as a rule of thumb for pistol barrels. Obviously rifle calibers are gaining speed at that length too.

 

[MachIVshooter]

A typical handgun round (9x19, .40, .45 etc.) doesn't gain much with barrels over 5-6 inches. The average gain for both 9mm and .45 in my own testing going from 5" to 16" barrels was between 100 and 200 FPS, depending on bullet weight and charge weight/type. My guess is that most of the addional velocity was achieved between 5 and 10 inches, with the last 6 doing very little.


OTOH, big rounds like the .50 AE or .500 S&W burning 30+ grains of powder behind large, heavy bullets will benefit considerably in a rifle-length barrel.