Several good ideas....try different ammo and maybe a different shooter for a perspective.
With a barrel length of about 4" the velocity of the ammo shouldn't be a major factor (longer barrels and slower ammo equals higher POI vs POA), but at 25 yards you never know.
I had a Ruger .44 magnum with a 7.5" barrel the would hit dead nuts at 25 with magnum ammo, but wouldn't hit the target at all with feeble 248gr .44spl loads......the recoil was effecting accuracy because the gun was already moving up in recoil before the bullet left the barrel.
If the same loads you are using group well at 5yds, move to 7, then 10, then 15, and 25...checking grouping at each range.
Maybe sandbag the gun on a bench and note whether the groups are rising with distance. Shooting from a rest may also help determine if it is your trigger control also.
Good Luck and safe shooting!!!