@CCT125US, I have not tested for expansion. They are marketed as expanding by RMR. What I can say is they are very accurate and pretty consistent with weight/diameter. They also feed extremely well with anything I've shot them through. I like them better than anything else I've bought from RMR and when I bought 12K of them the price was very reasonable for what I felt I was getting. I've shot about 7K of my order and will order more. Hope this helps tip the scales for you.