Here’s a question I haven’t seen in the two years I’ve been visiting your site.
How do the shotshell manufacturers and reloading component makers measure velocity? And, does barrel length significantly effect the velocity of a specific load? If so, is there a standard that we can use to calculate velocity loss/gain by the barrel inch?
SAAMI (Sporting Arms and Ammunition Manufacturers Institute), a manufacturers trade group, set the standards for measuring American ammunition. 12 gauge shotshells are measured from a 30″ barrel (I’m not sure about sub-gauge) for velocity at 3 feet.
The chronographs the manufacturers use are more sophisticated than the “hobby” chronos that people like me use. My chrono only measures the lead pellet. The serious ones in the labs measure the three feet from the average center of mass of the shot cloud. This makes for a very slight difference in shell speed, but not very much.
Be aware that other countries measure their velocities in different ways. For example, the high velocities claimed for some English and Cypriot shells reflect their method of measurement and will be slower when measured by the US standards. Off hand I can’t think of any country with a more conservative measuring system than ours.
The effect of barrel length on shot velocity depends on the type of load you are using. Most target powders behind relatively light target loads burn quite quickly and develop full velocity within the first 20″ or less of the barrel. Very heavy field loads and most steel powders burn for a longer time and may be more affected by barrel length. A good average velocity loss is 15 fps for every 1″ under 30″, but loads will vary. As do we all.
The Technoid writing for Shotgun Report, LLC
(Often in error, never in doubt.)