I hope the new brass resolves the issue. All the brass I have been using for the last 15 years on my 309JDJ, 338JDJ#2 & 375 JDJ has been R-P. If the R-P brass works for you, I would like to see if the Starline brass would fit in any of my barrels after being loaded. I would like to try a few pieces of the Starline and if it works, I would purchase from you if you wanted to do something like that.
I have a 6.5JDJ barrel I'm dealing with right now that after firing some rounds, I can't get them into the dies, to resize. The brass just past the rim after being fired is about .004 to large to fit into my old RCBS dies. So I just ordered a new set of Hornady from SSK and the brass won't size in it. After lubing fired brass, I can run the brass into either die about 1/8" at a time for about 15 strokes to get the brass sized to .421, which is what all chamber drawing show it to be. I have pulled many case rims off trying to size. I have gotten pretty good at removing stuck cases from the dies. This is on an older barrel I picked up a few years back and have just dealt with it. I found another 6.5JDJ barrel, RCBS dies and some brass on a site this summer and purchased it for a great price. All fired brass will work on either set of my dies with one stroke. This is when I decided after doing considerable measuring on brass, new, sized, fired that the barrel is letting the brass expand to much about 1/4" from the rim. I just sent the barrel, new dies, some fired brass from this old barrel and then some brass fired from my new barrel to SSK a few days back. I figured, what the heck. It's just laying on my work bench, taking up space. I wrote a 4 page letter with all of my findings and will be waiting to see what happens. I have been loading for my jdj rounds for 20 years and other wildcat stuff longer. This has been a venture to say the least. Will see what SSK has to say. I like all of my JDJ rounds and this is not bashing them in any way. Just want to know what they think it might be.

Good luck with your barrel and loading.

Mike

You don't quit playing because you get old, You get old because you quit playing.