To be able to decide which ammunition that is good is by trying it in your rifle. Major shooters usually go the the factory and try the ammunition there. For a normal shooter, the best option is to buy hundred shoots of a few different lots of match ammunition and then try it in the rifle. To be able to come up with a good conclusion about the difference in the different lots, the shooter has to make sure that the ammunition is shot in identical conditions. The ideal conditions is no wind and average light.
Many shooters prefer using a rest and scope on the rifle when testing ammunition.
The rest allows the shooter to hold the rifle totally still, while the scope makes the consistent aiming easier. Just make sure that the scope is a little bit off, so you don't shoot away the dot you are aiming at. If one would go to the factory to try the ammunition, the average 10 shot group from 50 meters for the best fit in your rifle would be in the 13-14 mm range. These test are done in perfect conditions - indoor using a clamping vise.