Being a sad muppet (and very bored at work) I measured the head sizes of about 20 JSB pellets both 4.52 and 4.53. What I came across was that the stated head size did not seem to match what I was measuring. 4.52's - 4.48 average (Skirt end 4.62) 4.53's - 4.48 average (Skirt end 4.65) So does that mean then the die using is incorrect or is it due to shrinkage was the material is warm when worked. Theoretically then there is no difference but there must be for them to say there is. What I need to find is an adjustable sizer to try different sizes and see if the groups improve. Before my rifle played up on Sunday I managed to shoot a very small group with Bisley superfields at 50yds (hieght difference over 10 shots was 14mm straight from tin). Maybe measuring the head size of those might help.