Shooting Lingo – Group Size

This sort of thing appears with some regularity on the forums, product reviews, etc., so I can only assume there is a significant number of people who don’t quite understand how a shot group on a target is measured.  What I recently read on an ammo review is that, since the bullet is x diameter, your group size cannot be less than x.

That’s not how it works. (Boomershooters bear with me, I’m pretty sure you all know this)  For the size of your group on the target, you’re measuring the center-to-center distance between hits.  If your holes were clean enough to allow such precise measurements, it is in theory possible to have half-inch diameter bullets and a group size of a hundredth of an inch or less.  You could just as well, theoretically, have an eighteen inch Navy ship’s gun that shoots a group of 1″ (all rounds through the same hole, to within one inch of center).  Actually getting a gun and several projectiles to do that is of course another matter, but it wouldn’t violate the simple theory of taking a distance measurement on your target.

This isn’t rocket science.  Well, maybe some aspects of shooting are in fact rocket science, but measuring the distance between centers of a few holes isn’t complicated, and has nothing to do with the diameter of the holes.  Any carpenter, machinist or cabinet maker, etc. knows this, and it is often learned by farm mechanics in early childhood.

5 thoughts on “Shooting Lingo – Group Size

  1. Yeah, but a holes-touching group punched out with .45 SWCs looks so much cooler than the same group punched with tiny .22 holes that seem miles apart.

  2. Seen the difference in a match between winning and 5th place to be on the order of 0.033″(winner was 0.144″, 5th was 0.167″). That was in the 100 yard lightweight division. Mostly done with some permutation of the 6mm PPC cartridge case.

  3. I did not know that. All these years, I’ve thought the term applied to the maximum diameter of the group, rather than the spacing on-centers. Live and learn.

    M

  4. As a practical matter, isn’t the longest distance between 2 hole “edges” measured, and one bullet diameter subtracted, to get the center-to-center distance?

    Of course, all I know about measuring groups was what I learned from watching the “Turkey Shoot” scene in Sergeant York.

  5. Mikee that is the standard method. Make sure to measure from the edge of the “grease rings” left by the bullet on the paper. Or just use OnTarget (http://www.ontargetshooting.com/index.html) Its free!

    I’ve seen some tactical rifle makers whose guns are shooting 1/10″ groups with .308 and .223 factory match ammo!

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