Velocity question

[taylor]

If a loading manual lists a formula that will push a 255grn bullet at 1000fps through a 6" barrel, how can I determine what it would do through a 3" barrel.
How much does velocity drop minus per inch?

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[Mark W.]

Most likely the first thing it would do is destroy your accuracy. I have found with my short barreled revolvers that the more powder burning out past the muzzle the less accurate the load is. I would assume the unresricted pressures push the bullet around in those first few mm past the muzzel effecting the spin and the bullets yaw.

You can tell with a Chronograph

 

[Collateral]

There is the math-heavy way - <broken link removed>
- or -
Read about what others have found during their tests at BBTI - BBTI - Ballistics by the Inch :: Calibers/Cartridges

 

[taylor]

Thank you for the link. Its about what I figured; going from a 7" to a 2" a cartridge loses about 1/3 of its velocity. Its hopeless to think I can get 800-900fps out of a 45lc 2"barrel w/o blowing the Taurus revolver to bits.

 

[deadshot2]

After using all the "calculators", "Rules of Thumb", "formulas", and "my Uncle told me's" it's all going to boil down to what happens in the actual firearm.

Shorter barrels don't utilize the benefit of a full powder charge. One needs to use a faster burning powder which then will build pressure faster yet in order to overcome the inertia of the bullet that pressure spike may damage the firearm. Longer barrels let the bullet start moving and then be accelerated by the building pressure of the slower burning powders.

Rather than trying for higher velocities, consider using a bullet that performs well at lower speeds or a lighter bullet that will gain some speed in a 3" bbl. If for SD hollow points are not only great, for some reason they also tend to be more accurate, at least in my "shorties".

 

[taylor]

Gold dot makes ammo for 45acp short barrel, it has great velocity for a 230grn bullet and expands rapidly. I don't know if they sell the bullets for reloading but using them and starting with an upper range load of Clays or Unique I'd be interested to see what results I get through a chronograph.