There is an excellent article at the end of the Oct 2014 Shooting Sports USA on group size and accuracy:
http://www.nxtbook.com/nxtbooks/nra/ssusa_201410/ This foundational article was written by small bore prone competitors who wanted to shoot perfect scores. In small bore prone a Match is a 40 shot event of two twenty shot targets. The typical 1600 round Smallbore bore prone tournament is 160 rounds fired for record, divided up into four 40 round Matches. herefore the referenced article assumes that a 40 round group is the baseline.
As anyone can see in table six, at least at 100 yards, a five shot group is 59% of the size of a 40 shot group, a 10 shot 74%, and a twenty shot 88%. A three shot group is below contempt, but three shot groups are the current standard for the shooting community because the leaders of the shooting community, that is in print Gunwriters, have convinced the shooting community that three shot groups are an exact measure of accuracy and consistency.
What we should recognize is that Gunwriters are shills for the industry. They really don't want to exhaustively test the weapons they are given for several reasons. The first is time and materials. Gunwriters are given a flat fee for their articles, the less they shoot, the less they spend, the more money they get to keep. The less time and material they have to spend on the current article, the more time and less money they have to spend on the next. That is one reason, and another is because even though these guys get weapons that are "worked over", they are not interested in proving the inherent accuracy of the thing, because the inherent accuracy of the thing may not meet the communities' expectations. Given the decades of constant repetition of the three shot groups in print, it is no wonder that the shooting community pretty much embraces it as the golden standard. This is a one example of how advertisers shape and mold society. There are numerous other examples, such as the diamond engagement ring, and how all Christian holiday's have turned into "gift" giving holiday's. If you love someone, you buy them something, and if you really love them, then you must buy them something really expensive.
Eley came to one of the Smallbore Prone National Matches to give a sales pitch for their in door range. Eley did address the rim measurement question by putting up a chart of all the characteristics they measure and control. There must have been a hundred. But this is also match ammunition. That level of quality control is not to be found in bulk ammunition. After seeing the number of characteristics they measure and control, it was obvious to me that the prevailing idea that someone can measure one ammunition characteristic, other than group size, and see an improvement, is based on small sample sizes, confirmation bias, the Texas Sharpshooter fallacy and probably other fallacies . There is nothing evil going on here, it is just that humans see what they want to see. It is the way our minds work. Humans see patterns were none exist, and this idea that accurate rimfire rounds can be pulled from a population of inaccurate rounds, by any means other than shooting, is based on small sample sizes and the human bias to see patterns where they don't exist. Literally millions of gamblers think they have a "system" which allows them to beat the Casino. In the long run, gamblers always loose against the house, but in the short run, the occasional win allows gamblers to think that their "system" is working. Same thing for those who conduct rim measurements and think they see an improvement. The only way to see an improvement on target, is to shoot enough rim fire ammunition to statistically prove an improvement. And that takes testing at the range.
I have seen radical differences in group sizes with different brands of bulk ammunition, but, once you shoot up the lot of your best bulk ammunition, there is no guarantee the next lot of the stuff will shoot as well. And bulk ammunition has never been as consistent as match ammunition, even the cheaper grades of match ammunition.
Eley has a 50 meter range in the US and Lapua has a 100 yard range. I have been to the Lapua range for lot testing of ammunition in one Anschutz rifle. Both entities shoot 40 shot composite groups for the most promising ammunition. What was amazing to me, was to see the differences in accuracy between lots of "similar" quality. Eley told us, they did have separate production lines for their various ammunition brands, and the most QC is conducted on the Red Box and Black Box lines. At the end of the line, lots are sorted into Red Box (most expensive) and Black Box (less expensive but still hideously expensive) by which lots shot best in the range test barrels. . Eley was rather dismissive of questions about which barrels they use, and I believe it is because ammunition lots are more variable than match barrels. At least that has been my experience with match rifles. Shooters will find that different lots of the same quality ammunition shoot differently and the differences are quite large. A shooter who placed third in the Nation that year, told me that lot tested ammunition then had to be shot in position, because results off the machine fixture were not necessarily indicative of how the ammunition did prone Ammunition makes more of a difference on target than a particular barrel brand, assuming a good barrel, good chambering job, and a steady rest.
An F Class shooting bud gave up on TAC22 after this target. He was continually frustrated with the inconsistency of the ammunition. but this 12 inch dropped shot caused him to walk to Eley Black Box ammunition.
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Same gun, same distance, different day of course, but Eley Black Box ammunition. Bud is now shooting rounder, more consistent groups.
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This is a recent example, to me, of the difference between good rimfire ammunition, and lesser quality rimfire ammunition in a match rifle. These groups were shot in the same match, same rifle. This Center-X ammunition is good stuff. While this is not a 100-10X, this ammunition is showing potential in this rifle.
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This SK Rifle Match shot well at fifty yards, but at 100 yards, I am 100 % certain that the 6 O'C shot was not due to me, could have been due to a wind change, but overall, I have had enough of these dropped shots with lesser ammunition to be confident, this is just something that happens with cheaper ammunition.
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I have shot enough of the good Center-X in other rifles, that I have a great deal of confidence in its consistency. It consistently shoots round groups and I have not experienced dropped shots like I have seen with cheaper match ammunition. And I think that is the primary difference between the different grades of match ammunition. The higher grade stuff is more consistent, though, it is not unknown to have a flyer that cannot be explained, and the flyer tends to be closer to the middle than a flyer from cheap ammunition.
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SK Standard Plus is even a cheaper grade of ammunition, shot a nice group in my Kimber, but that low velocity shot with Eley Club is something you will occasionally see with the lesser grades of match ammunition.
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I have shot enough ammunition and seen enough 6 O'C dropouts with cheaper ammunition to believe, that it is a real phenoma, and that it happens much more often with cheaper ammunition. I have shot the awful stuff they issue to Juniors, I think it is CCI Standard Velocity, and I could not hold the ten ring at 50 yards in my match rifle. I have not scanned any of my bulk ammunition targets, I only use that stuff for getting on paper when zeroing a rifle and for calibrating my chronograph. I have to say, my case of Remington Target Match is some of the most unreliable and inaccurate ammunition I own. I have blown about half a case of Green Tag downrange and was not impressed.
Last weekend I shot CCI SV in my Ruger MKII and had an alibi during timed fire. The round failed to eject. The case was so low pressure it never left the chamber. This is new ammunition, bought it last year, from the case at the LGS. I had no idea which hole the alibi round put in the target, and based on my ability to shoot Bullseye Pistol, I don't have the ability to sort out good rounds from bad rounds offhand with a pistol. So, cheap, bulk rimfire ammunition is just fine for me, with a pistol, as long as it always goes bang!
