The only way to be certain of your pellet size is to put them through a sizer.
The "competition grade" pellets may be more consistent than the cheaper offerings, but to be sure and confident, it would be best to mike a good number.
When I checked a selection of pellets a couple of years back, none of them corresponded in any dimension with what was printed on the tin, even the AA Fields. I measured head and skirt, both over two diameters, 90 degrees apart.
Then I bought a sizer from UK Neil!
Walther CP-2 Match, FAS 604 & Tau 7 target pistols, Smith & Wesson 6" & 4" co2 pistol, Crosman 1377,
Baikal IZH 53 pistol, Gamo CFX Royal,177, Umarex SA-10 CO2 pistol.