Velocity And Barrel Length


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?

Thanks, Dan

Dear Dan,

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.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error, never in doubt.)

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1 Response to Velocity And Barrel Length

  1. Hi Bruce. Interesting column as ever.
    I thought I could maybe clarify a point regarding the high velocity figures you can read on some (but not all) UK made cartridge boxes. These high figures are supposed to be ‘Muzzle Velocity’ and arose more widely when one maker thought it a good idea, some years ago, to put this ’rounded up’ MV figure on their cartridge boxes as it made them appear much faster that most opposition (UK or otherwise). Others had to follow suit as it was just confusing shooters. I’m not sure anyone can actually measure MV particularly well but, whether they can or not, its strange they always seem to go up in nice round steps of 50 fps (1250/1300/1350/1400 etc). Actual increments are seldom so tidy, as you will know!
    Anyway, my real point is that this is NOT how cartridge velocities are officially measured in the UK. UK is a member of the International Proof body the CIP. This is similar to your SAAMI but uses different methods and pressure etc. Maybe one day they will agree to come together on ammunition testing; who knows (they do have dialogue with each other!)
    The CIP rules stipulate that shotgun ammunition is measured at 2.5 metres from the muzzle (NOT at the muzzle). This is achieved using the specialist chronographs with shotgun timing screens that you mention; the screens are set at 2 metres and 3 metres from the muzzle of the Proof test barrel with the resultant velocity being given as the mean distance of 2.5 metres. Measurement is in metres per second which again makes the figure appear low compared with FPS. Some shooters understand this; others do not.
    So, in fact, the distance at which UK ammunition is OFFICIALLY TESTED and which I include in my ammunition tests as I use the Proof House to test ammunition I write about for Pressure, velocity, consistency (Std Deviation) and momentum (an indication of recoil energy) IS actually a GREATER distance than US makers use! Being approximately 2.5 times further from the muzzle than US makers use (the 3 feet you mention being roughly 1 metre) then those makers that state the CIP figure will appear slower.

    Keep it up; I do enjoy reading your material.
    Richard Atkins


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