I have also noted similar results as you from some JSB pellets. If I am not mistaken, the first two numbers in the series on the tin is the die number. So, your old pellets were likely die 30. I had good results from die 30 as well. However, your new pellets are likely from die 40.
I will bet if you look closely inside the skirt from the back of the pellet, the die 40 are probably deeper and end with a near pin point shape. In contrast, the die 30 will be shallower, and end with a blunt, flat spot inside the skirt.
Good luck in finding something to replace those old faithful die 30's.