I understand what you're talking about when it comes to testing ammo for "LOT #"s" and not BRAND or BRAND TYPE. It's also understood that different LOT#"S may perform better/worse so you have to test. BUTTTTTT....... certainly SOME ammo NAMES do have a reputation for performing better with most ACCURATE rifles. I wouldn't expect S&K STD to perform as well as Centre-X. Yes, it has given excellent +++ results on 1-2-3-4 targets BUT it will still produce more "flyers" than Centre-X, and most groups are about 1/8" larger @50 yards, at least in my experience. When the good bench shooters decide to test for accuracy what ammo TYPES/ BRANDS do they usually start with???
I don't know how good bench shooters explain this but I'll give it a try. Please forgive the length, but it does have pictures to help.
It's true that some ammo names/varieties have a reputation for performing better than others with most accurate rifles. Remember that this is on average. You would expect that,
on average, more expensive ammo varieties,
should perform better than less expensive ammo variety. For example, Lapua X-Act should perform better than Lapua Midas + and Lapua Center X -- on average.
Why? These Lapua varieties, like the Eley flat-nosed varieties Tenex, Match, and Team, for example, are made on the same machinery. (For simplicity, I will refer only to the standard rifle match ammos, and leave biathlon-specific and pistol ammo to another discussion.) What distinguishes one variety of Lapua or Eley from another are the quality control standards which they meet. The best is X-Act for Lapua, followed by Midas +, and finally Center X. The same happens with Eley with Tenex meeting the highest standards, followed by Match and Team, respectively. In this process, the best ammo variety has fewer lots produced in a given production run than the other varieties. In other words, Lapua produces more Center X than Midas + or X-Act.
The thing is that despite being produced to higher standards of quality control, there's no way for the manufacturer to guarantee
how a particular lot will perform in any rifle until it is tested. The big three match ammo makers -- Lapua, Eley, and RWS -- all test their products. Eley used to have an on-line "Lot Analyser" that showed their test resultsin four different barrels for all lots produced.
Below are some examples of seven random lots of Eley Tenex, the top-tier Eley ammo. The images show four columns, one for each test barrel. Each column shows the results of five ten-shot groups. These results are obtained with the barreled actions in an immovable vise/fixture and the shooting in a tunnel with the results scored electronically.
These results are with Eley Tenex, the "best" that Eley produces, tested in a tunnel with the barred action clamped down. Each ten-shot group shows some of the results that are possible out of 50 rounds (one box). It costs close to $250 per brick at current Canadian prices. One lot seems best, but if there are seven lots at the dealer from which to choose, can you get the best one by having the dealer pick randomly for you? It's not often that a Canadian dealer would have as many as seven different lots of Eley Tenex on hand for shooters to test.
Obviously some lots are better than others across all barrels, and obviously some lots perform better in some barrels rather than others. But it's still Eley's cream of the crop ammo. Eley no longer has the Lot Analyser available on-line. Why? It probably didn't help clarify things for many shooters. They probably were looking for particular lots that shot well in all test barrels. No doubt when such a lot was identified, there was a rush to find it. If it wasn't readily available -- and the number of cases produced of any top-of-the line ammo would be relatively small, probably less than ten, the result would be frustration. In any case, the Eley Lot Analyser has been discontinued.
If a shooter wishes to find a good lot of ammo, he might do well to regard the search as one that is similar to looking for a good car. Everyone knows that on average some cars are better than others. Without pretending to know current auto ratings, let's say for the sake of argument we are looking for a second car for the family, a used one, something like a Honda Civic or a Toyota Corolla, two models that on average generally have a very good reputation for reliability.
The best time to go to the used car dealer, who gets used cars periodically on auctions from across the country. The best way to get a good car is to shop when the dealer has many candidate cars from which to choose. Some may be eliminated on the spot, but test driving them will help make the decision. Furthermore, if you can take some possible candidates to your trusted mechanic, the choice would be easier. You therefore have a good chance of getting a good used Civic or Corolla if you take the appropriate steps of shopping early, test driving, and taking the candidate cars to a trusted mechanic for a closer look.
If, on the other hand, you shop late, when the dealer has few choices of Civics or Corollas left on his used car lot, you are taking a greater risk of getting a car that is not as good as some of the other units the dealer previously had available. In fact, when there are few individual ones available, the ones not chosen by those used car shoppers that were able to pick over the other cars available earlier, the odds increase that those few may not be the best ones that the dealer has had.
All the cars are either Civics or Corollas, models with good reputations for reliability, but each individual car may not be exactly the same as the others. Ammo is like that too. Center X may has a good reputation, but not all individual lots of Center X are the same as the others. Like looking for a good used car, you have to test drive the ammo to make sure it's good for you and your rifle.