I don't think that your fouling problem is caused by bullet characteristics or your twist rate. I think the most likely culprit is the factory barrel. There is likely some roughness in the barrel that is causing your fouling problem. The barrel may smooth out with continued shooting and cleaning.
If not, you may wish to fire lap your barrel. I have had to do this with two of my rifles and had good results in both cases using Tubbs' Final Finish.
Where the cleaning is concerned, I would recommend a good foaming bore cleaner such as Wipeout. It will save you a lot of frustration and will get your barrel much cleaner with a lot less "elbow grease."