204Ruger

If you are still having trouble I would lube the inside of the necks prior to sizing, if you use wet lube on a q-tip you will have to tumble them to get the lube off, might want to anyway for the lube on the outside of the cases. If that doesn't do it and all the above doesn't help, TX204 mentioned the crimp, the seating die might be buckeling the case slightly just below the shoulder, raise the body of your seater die up a quarter of a turn, rememder to raise the seating depth plug accordingly.

Yes My steel mags have a ridge or bump on each side. when a bullet is slamed forward those are often a bit sharp. Bye filing the edges more rounded and smooth I have eliminated denting.

It does sound to me like perhaps your gun was chambered tight kneck to a factory case and perhaps not to a go gage. This would be unique to a factory gun? Doesnt make allot of sense but could reamer have been worn when barrel was reamed? I am grasping at straws. There is no reason you shlould have trouble reloading for a ar. are feed ramps on barrel sharp? Is brass ejecting properley or getting in way of secnd round? Is your rcbs die adjustable? Do you know someone who could loan you a different die? Perhaps the die is the issue. A problem with your die seems most likley to me?

I used to have this problen on some of my reloads and I filed the shell holder down just a .001 or so and that bumped the shoulder back a lttle more. No problems since then.

Jimmy