Would you possibly do better going to a somewhat faster powder to complete the burning and the lessening of the pressure sooner - before the bullet reaches the muzzle? The effect of the high pressure gases to tip or push the bullet upon exit from the muzzle could be a factor here.
The narrow bore in a .25 caliber is awefully constricting and delays the consumption of the powder, too. Powder burn rate is a big consideration, but so, too, is the bore.
I would also, as said before, consider changing the stock, too.