Shot Size Designation
There are a multiplicity of shot size designation systems around the world. The one used in America is known as the American Standard system and is adopted by SAAMI, the Sporting Arms and Ammunition Manufacturers Institute located in the U.S.
The American Standard system for shot size designation depends upon the magic number 17, designating shot sizes in hundredths of an inch. For example, by the American Standard system, a pellet designated as No. 6 size, regardless from what material it is made – lead, steel, tungsten, bismuth, whatever – is a pellet .110 inches in diameter (17 - 6 = 11).
Diameter Variation Tolerance
As to allowable diameter variation tolerance, SAAMI voluntary performance standards state that game shot (actual shot sizes falling into this category undefined) are allowed a nominal diameter tolerance of ± 0.010 inch, target shot (again actual sizes undefined) are allowed a diameter tolerance of ± 0.005 inch and buckshot (shot sizes defined as No. 4 Buck through No. 000 Buck) are allowed a nominal diameter tolerance of ± 0.015 inch. So a pellet made in the U.S. in the game shot size range could vary a full pellet size designation either way (remember: the variation tolerance is ± 0.010 inch) and still be called that pellet size. Example: according to SAAMI a group of pellets could vary in diameter from as large as No. 4 to as small as No. 6 and still be honorably represented on a bag of loose shot sold for reloading in the U.S. or loaded into American factory ammunition as No. 5 shot. Things get tighter for target shot (typically thought of in the U.S. as being No. 7 pellets or smaller), as the allowable diameter variation tolerance is only a half size (± 0.005 inch). But hey, when you think about it, you want to be pretty discriminating about so-called No. 7½ or 8½ shot for according to SAAMI voluntary performance standards for target shot, a group of pellets could vary from as large as No. 7 to as small as No. 8 and still be designated as a No. 7½ by the manufacturer. In like manner, so-called No. 8½ shot could be as large as No. 8 to as small as No. 9 and still be designated a No. 8½.
Personally I would not consider shot loaded in factory shotshells or bagged for reloading as being a truly quality product if the actual diameter of a 25-pellet sample varied more than ± 0.004 inch regardless of shot size category: game, target or buckshot. And, for little 7½’s or 8½’s, I wouldn’t want to see the variation greater than ± 0.002 inch, or buying these half sizes becomes meaningless.
Concerning shot roundness or sphericity, I can find no standards anywhere in the U.S. for this important characteristic of shot quality. The matter is simple: if a pellet is supposed to be approaching a spheroid as the desired shape, then the rounder or more spherical the actual shape of the pellet, the truer to the point of aim it will fly, the better will it retain its energy, and the better it will penetrate. Round shot also patterns more densely than out-of-round shot. And if round shot can arrive on target round, then it presents less surface area than a non-round pellet of the same diameter which translates into better penetration potential.
Since there are no standards in the U.S. for pellet roundness, a manufacturer or advertiser can use the word “round” to mean anything these entities want. What it usually means is they are calling the product round because to them they consider their shot round. But to you the shotgunning consumer, I wouldn’t advise taking any claim of “round” as literally true. After all, first, unless a pellet is cast and then perhaps polished we have no means of making a truly spherical projectile. Those stylized cross-sectional-view drawings of shotshells depicted as containing perfectly round projectiles are laughable. By the tower dropping or Bliemeister methods currently used worldwide to make lead shot, we ain’t never made a truly round pellet.
Secondly, the only way most tower-dropping manufacturers of lead shot have of grading and sorting for roundness is to use tilted glass or steel plates. But even this method still results in a fairly high percentage of non-spherical pellets making it into a factory shotshell or bag of shot sold for reloading.
So my advice for the discriminating shotgunner is to take nothing for granted relative to pellet sphericity based on the word “round” appearing on a box of shotshells or a bag of loose shot. The best way to get a sense for the degree of sphericity of the shot in the factory shotshells or bag of shot in question is to do your own visual evaluation by rolling shot across a slightly tilted glass plate.
In Part 2 we’ll finish up by examining in detail shot hardness and plating.
Copyright 2013 by Tom Roster. All Rights Reserved. This material may not be published, broadcast, rewritten or redistributed.