Thread: Case capacity effects on velocity

Yup hamsav, nowhere near shooting one hole groups... There is this nigly little thing called wind

Found some interesting comments here : Internal Ballistics

By using a cartridge case with greater capacity we provide for more chamber volume with the same bore volume, thus the expansion ratio (see definitions above) becomes less. As a result, the powder gases have been through less expansion by the time they reach the muzzle and muzzle pressure is higher. As the muzzle pressure is higher, the average pressure along the bore is higher and the bullet has a higher velocity. There is a trade off for this. Because the muzzle pressure is higher, more energy is carried off into the air unused (as flash and muzzle blast) and thus the efficiency of the load (the getting of energy out of the powder charge) is less.


You get the same effect with seating depth, further down, less pressure and velocity.