Only occasion I had cause to "size" .25 Cal. pellets was for a BSA 635 Magnum and a Superstar. Both were .243 Caliber.
I used .25 Rhino, Marksman, Bis. Mag, Superfield and F&TT.
The latter turned out to perform best i.e. tighter groups.
I did however once own a .25 BSA Lightning Tac XL with what must have been a "true .25 bore" as it accepted and shot un-sized F&TT's really well !
I only have one "quarter bore" air rifle nowadays, a smashing SFS HW 80k which shoots unsized F&TT's with good accuracy !
“Let us not dwell on the distance we have fallen short, let us dwell on the distance we have travelled" !