sizing die

I always calibrate my mics and calipers prior to slugging a bore.

To account for the 6.25mm land, 6.34 JSB pellet head, and 6.44mm groove sizes, I went back and measured a US cent with my digital caliper. It's right on 19.05mm which is the official size. Of course I can press real hard on the caliper and get down to 19.02mm, but the measurement returned to 19.05mm. I measured with the wider/inside surface of the caliper and the outer/thinner surface. The outer/thinner jaws are trickier to measure, but still came up with the same size in the overwhelming majority of times as I was trying various placements of the penny inside the jaws.

So, I need to go back and re-slug the barrel to confirm if my original measurements were correct. May break out my 50x microscope I used for coin cleaning or get a finer outside (spring joint) caliper.

LW .25 barrels are .248" land .254" groove. So, it is highly plausible that CZ also uses a slightly oversized groove of .252"? Unfortunately those sizes make sizing most pellet heads to groove impossible.

I will check the choke sizing. I am assuming that the grooves get reduced inside the choke from whatever that size was in the barrel. I think that's where the trick is. It must be at or less than 6.34mm or 0.249

Choke size isn't relevant to what diameter to size pellets too. By the way, a choke is a bandaid for the lack of consistancy in pellets.