Effect of Crimp Depth on Shotshells

Crimp depth of a finished shotshell reload is an important dimension to monitor for consistent ballistics and safe loads. This is one adjustment on a shotshell loading machine that is easy to overlook. An example of the correct crimp is what is found on factory loads. If your reload crimp is too loose (not enough crimp depth), it will hurt ballistic uniformity. A crimp that is too tight (too deep) can increase ballistics more than what is expected from the reload data. All shotshell reload data on the Hodgdon website has been created using an average crimp depth of 0.055".

As an example, here are ballistic test results of a standard 7/8-oz, 12-gauge load when crimp depths are varied:

Crimp Depth  Velocity Chamber Pressure
0.030" (too loose) 1,308 fps 9,300 psi
0.050" (normal reload crimp) 1,329 fps 10,500 psi
0.070" (too tight) 1,351 fps 11,900 psi
0.090" (very tight crimp) 1,363 fps 13,100 psi

         

This data was created in the Hodgdon Ballistics Laboratory under controlled conditions, and only the top two loads show pressures that stay within the SAAMI industry standard of 11,500 psi.