If you are measuring 0.306-0.307" on the skirt of a pellet that was pushed through the bore, then the bore is at least that big.... The FX Pellets I have here measure 0.300" head and 0.308" skirt fresh from the tin.... It would appear your barrel is a whisker tighter than the LW barrel I have (0.300" lands - 0.308" grooves), but a lot bigger than the new barrels Sean and I had made for the JSB/FX/Daystate pellets.... Our barrels are 0.294" lands, 0.300" grooves....
Bob