You never did say how old your rifle is or approximately how many rounds you had through it.
And I am assuming you cleaned your rifle on a regular basis but maybe not with the right products. And assuming that you shot copper jacketed bullets you may be experiencing a buildup of copper fouling. I don't care much for the ammonia based copper solvents but I have found that Hoppe's Elite Copper Solvent to be very good at removing copper. Run a saturated patch in the bore and let set for 10 mins then wipe out. Do this several times until the patches come out clean.
If you're still having the accuracy problems after this I would then use the J-B Compound per the manfs. instructions.
And the previous posters are right about the Dewey rods. Those things are great and last forever.