I have used them on several rifles, all of which will put 3 shots easily within a 1" group. I did not compare loads before and after, so I am not saying that they improve accuracy, but it does give me peace of mind. I will say that they do make it easier to clean the barrel, which you will notice when you get to the third set of bullets. I would probably not use them on a custom barrel, especially if the barrel had been lapped. I still have the bullets for the Tikka 6.5x55, so I may do a real "before and after" comparison when time allows.
