I thought they might be, 4.52 & 5.52 are the common size which seem to fit 90% of anything out there. I’ve got a custom made 0.22 pellet sizer somewhere, not sure if that will have any effect on the heads, probably only does the skirt.
It might be a case of trying some JSB Exacts in 5.51 or 5.50
I’ll nip over to the Chinese UK forum and see what pellets are commonly used by other DB4 / DB5 owners
Norm