I'm a bit puzzled. Just picking on my .257 Roberts, I am full-sizing brass which has been loaded 10+ times. Even after a full-size with RCBS dies I'm finding that the bolt on the rifle is very tight to close.

Compare this to brass that is new or fired once and there's almost no effort to closing the bolt.

One presumes this means brass is stretching in some way that a Full-size isn't correcting.

Thoughts?

PS: accuracy is still very good at 3/4" groups at 100 yards. The load is 46gr. H4350 and a 100gr. SGK. Warm but not hot. Ejection is clean, no sticky bolt or anything. No pressure signs.

It sounds like your brass has been work hardened by repeated firing and resizing cycles.

You can try double sizing by
1. Sizing the case as normal but very slowly and let it dwell at the top of the stroke about 5 seconds to let the brass move.
2. Without pulling the case out of the die pull it down enough to turn it 180 degrees and size again. Again let it dwell.

It will probably chamber now.
I would suggest that you investigate annealing the necks and shoulders of your cases. Done properly your cases will go back to behaving more like new brass.

Also check the length of the cases and trim if necessary, If you haven't trimmed after ten firings then they may have grown too long to chamber and if forced may cause pressure problems.

Cheers, Chris

Any marking of the base? Hot loads can push brass "backwards" yielding extractor marks -- they look shiny.

#1 The web has expanded from repeated firings? Photos photos

Make sure your die is bumping up hard against your shell holder. I like a little bit of cam over when I want to really full length re-size. If that does not work, you can lathe turn a few thousandths off the bottom of your die. I have had to do that many times to solve your type of problem.
And anneal your necks and shoulders. Your loads are not hot at all.

Sometimes the inside expander will drag the
shoulder out a schoshi bit. Lube inside the neck
at the shoulder with a light dab of lube.
If you aren't using Imperial Die Lube this
is a good time to start.

If you haven't been you may need to trim your brass as the necks tend to grow until they meet the start of the rifling which will cause the symptoms you describe. It can also raise pressures.

Jerry Liles