Originally Posted By: PeteM
My understanding is that internal pressures in a shotgun peak about 16" from the chamber. So has the maximum velocity of the projectile been reached within the barrel?
Pete


The pressure in a shotgun barrel peaks within the first 1/4 - 3/4 inches. At 16" the pressure will be down in the 1000-1500 psi range and, say, 500-1000 psi at the muzzle. The base of a 12 gauge wad should be about 0.42 square inches. The thrust on the payload near the muzzle, then, would be 210-420 force pounds. Acceleration would be thrust minus drag. The payload will continue to accelerate until thrust equals drag. We know that thrust and drag are getting close as the loss of velocity from shortening a shotgun barrel is small.

If a shotgun barrel is over-pressured, the burst will occur at the first point where the hoop stress exceeds the ultimate strength of the barrel steel. Depending on how the barrel is bored and profiled, this could be anywhere along the entire length. Had the chamber walls been thicker in J-C's example, the burst could still have occured further forward as in revdocdrew's example.

Last edited by Rocketman; 09/09/08 11:17 AM.