Funny. My gym claims all their BBs are 50 but one which is 45 pounds. The 45lb one in question is clearly thinner and seems to weigh less but I just chalk it up to my mind playing tricks on me. One of these days I will weigh them all. So there is a decent chance that most of my PRs are actually 5 lbs more!
Nice.
The difference between the 65's and the 45's at my gym are the fact that the 45's are smooth and slightly thinner, while the 65's are a little fatter and have ridges on them.