Whenever I run into a problem like this, I go back to the basics and proceed with the process of elimination. ...
1) I go back to a good known factory RB.
2) I mike my patches to determine if they are out of spec. I usually stick with .015 Lubed
3) On the bench for target; I clean between every shot. Every fifth time for fun.
Would add that the last class we taught, all of a sudden, my PRB's got tight. I was using the states patches which were labeled as .015. Went back to my patches and they loosened up again. Took some samples home with me and found that they were oversized, just just enough to be a problem. ....
Now, I run my own lead and when I run RB's, I always make certain that it is pure lead. I roll check, weigh and mic. them. I lay these aside for target use. The others that are not so good, I keep for fun shooting or classes. Some are completely rejected. ...
A pure lead PRB, is very forgiving and easy to work with. When loading, they yeild quite easily. ...
Be Safe !!!