You might try loading a box with unsized, hand lubricated bullets. If that solves the problem, you need a bullet sizing die one or two thousandths larger.
If that doesn't solve the problem I'd have a smith check my barrel.
And I looked, and behold a pale horse: and his name that sat on him was Death, and Hell followed with him. And power was given unto them over the fourth part of the earth, to kill with sword, and with hunger, and with death, and with the beasts of the earth.