To achieve the best accuracy, shooters are often reminded to "find the ammo your rifle likes". What does that mean? Is a shooter to buy different kinds of ammo, and by shooting and comparing targets, determine the variety of ammo their rifle "likes"? Perhaps the smallest groups are with a certain variety of SK/Lapua, or RWS, or Eley ammo. For the sake of argument, let's say the best results after comparing a half-dozen or so ammos the best results were produced by Lapua Center X.
Is that it? Does that mean that if the shooter buys Lapua Center X he's good to go and can rest assured that he will have good-shooting ammo whenever he buys more Center X?
The best answer is a qualified maybe. The thing is that not all ammo of a particular variety is equal. Consider the example below.
This morning it was very calm so I decided to go to the range. It was only 2 degrees when I left but by the time I would finish it warmed up to near 7 Celsius.
I kept my ammo in the inside pockets of my jacket. I only took out five rounds at a time and kept the rest of any box I was using in an outer pocket while I was shooting.
My rifle was an Anschutz 1411 with a BR 50 stock. This rifle has given me the best results I've had this shooting season with the same make of ammo I would shoot today. Nevertheless, the results today are necessarily the best results achievable. Warmer, more comfortable temperatures in which to shoot has previously produced different results, indeed much better ones (at least on targets for which I have kept more complete records). In any case, even though the results are not particularly good, certainly not outstanding, all my shooting toda was done under virtually identical conditions, cool and quite calm, with the result that the comparisons between ammo should be more or less valid.
I shot two different lots of Center X and the results were striking. One lot of Center X, which while not producing especially good results, was considerably better than the other. I put the same effort into trying to obtain the best results for each round I fired, despite the unspectacular nature of the targets, which are shown warts and all.
The "better" lot:


The not-so-good lot:


The above results show clearly that not all lots of Center X (or other ammo) is necessarily the same. To be fair, most lots are average and will produce results that are average for that particular ammo. I have concluded that the more poorly shooting Center X shown above is a less-than-average shooting lot of Center X, probably considerably less-than-average lot. The better lot is somewhat closer to average, despite the uneven results.
The point I wanted to illustrate above is that different lots of ammo can shoot very differently. Most lots of a variety of ammo will be average, but some may be better and some may be worse. It's not so much about finding the ammo your rifle likes as finding the lot(s) your rifle likes.
It must be kept in mind, however, that different individual rifles -- even of the same make and model -- may shoot the same lot of ammo differently, that is they may get different results with the same ammo. In turn, ammo that is not especially good in one rifle may shoot better (or worse) in another.
As unsatisfactorily the worst Center X lot shown above shot, it was not the worst I've had the bad luck to have. I bought some Center X in August that shot even more poorly, and in milder temperatures to boot. The dealer sold it with the promise that he'd take it back if it wasn't good, and he did. The ammo that replaced it was better but not particularly good.
All told, I have had good luck and bad luck with Lapua ammo and everything in between. It's not the make or variety of ammo with which you will achieve your best results. I've had good results with Midas + ammo and bad results. I think I've shot all the "good" lots of Midas + I had at the beginning of the season. What I have left is decidedly unsatisfactory, as the results I obtained today with a box of what I have left shows below.

That's especially disappointing for ammo that costs $20 per box. On the bright side, this lot of SK Rifle Match is not too bad, if you can accept that it can't be expected to be as good or consistent as "good" Center X or Midas + ammo.

In the end, the quest for accuracy is about finding the lot(s) your rifle likes.
Is that it? Does that mean that if the shooter buys Lapua Center X he's good to go and can rest assured that he will have good-shooting ammo whenever he buys more Center X?
The best answer is a qualified maybe. The thing is that not all ammo of a particular variety is equal. Consider the example below.
This morning it was very calm so I decided to go to the range. It was only 2 degrees when I left but by the time I would finish it warmed up to near 7 Celsius.
I kept my ammo in the inside pockets of my jacket. I only took out five rounds at a time and kept the rest of any box I was using in an outer pocket while I was shooting.
My rifle was an Anschutz 1411 with a BR 50 stock. This rifle has given me the best results I've had this shooting season with the same make of ammo I would shoot today. Nevertheless, the results today are necessarily the best results achievable. Warmer, more comfortable temperatures in which to shoot has previously produced different results, indeed much better ones (at least on targets for which I have kept more complete records). In any case, even though the results are not particularly good, certainly not outstanding, all my shooting toda was done under virtually identical conditions, cool and quite calm, with the result that the comparisons between ammo should be more or less valid.
I shot two different lots of Center X and the results were striking. One lot of Center X, which while not producing especially good results, was considerably better than the other. I put the same effort into trying to obtain the best results for each round I fired, despite the unspectacular nature of the targets, which are shown warts and all.
The "better" lot:


The not-so-good lot:


The above results show clearly that not all lots of Center X (or other ammo) is necessarily the same. To be fair, most lots are average and will produce results that are average for that particular ammo. I have concluded that the more poorly shooting Center X shown above is a less-than-average shooting lot of Center X, probably considerably less-than-average lot. The better lot is somewhat closer to average, despite the uneven results.
The point I wanted to illustrate above is that different lots of ammo can shoot very differently. Most lots of a variety of ammo will be average, but some may be better and some may be worse. It's not so much about finding the ammo your rifle likes as finding the lot(s) your rifle likes.
It must be kept in mind, however, that different individual rifles -- even of the same make and model -- may shoot the same lot of ammo differently, that is they may get different results with the same ammo. In turn, ammo that is not especially good in one rifle may shoot better (or worse) in another.
As unsatisfactorily the worst Center X lot shown above shot, it was not the worst I've had the bad luck to have. I bought some Center X in August that shot even more poorly, and in milder temperatures to boot. The dealer sold it with the promise that he'd take it back if it wasn't good, and he did. The ammo that replaced it was better but not particularly good.
All told, I have had good luck and bad luck with Lapua ammo and everything in between. It's not the make or variety of ammo with which you will achieve your best results. I've had good results with Midas + ammo and bad results. I think I've shot all the "good" lots of Midas + I had at the beginning of the season. What I have left is decidedly unsatisfactory, as the results I obtained today with a box of what I have left shows below.

That's especially disappointing for ammo that costs $20 per box. On the bright side, this lot of SK Rifle Match is not too bad, if you can accept that it can't be expected to be as good or consistent as "good" Center X or Midas + ammo.

In the end, the quest for accuracy is about finding the lot(s) your rifle likes.