A recently purchased set of used RCBS carbide dies (45 LC) is excessively resizing case mouths down to .469" (outer diameter). The norm for this is .480".

Resizing used brass leaves a noticeable "shoulder" about a third of the way up from the case rim regardless of brass manufacturer (full length resizing is not happening here); brass must be "over-flared" to some degree in order to get the resized cases to accept bullets.

Phoncon with RCBS SC rep did not include any suggestion that the offending die be sent in for inspection/replacemet.

Is this die out of spec? Some cowboy shooter forums suggest that .45 LC brass doesn't need to be resized.

Any ideas?

Not above purchasing a set of new dies from another mfr.

@Gunman53

Call RCBS.  They have excellent customer service in my expirience.

(It would help to have ID measurements or brass thickness measurements to get a better feel for how undersized the brass is.)

You can flare the mouths back out right?

My RCBS dies in 45LC leave a bit of a neck also, but they fit my ruger, no problem.

I have to flare the neck out, I never measured the sized case neck, just did it and flare then load.

Cowboy action shooters use such light loads they maybe don't have to resize.

But if you shoot higher horsepower loads you have to resize or your bullets are going to jump out the case by the time you get to the 3rd or 4th shot

and tie up the gun.

That is a really strange situation. Can you post pictures of the dies and cases?

I thought that in most carbide dies for straight cases, the sizing is done by the carbide ring at the base.

If you're not Full length sizing and have many loads on the brass, I would consider that the chamber on your revolver is loose and that you're only tightening the neck to hold the bullet in place. The cowboy shooters I know generally don't full length resize because  they get more loads out of the brass and they're only getting to above minimum velocity, which saves money on buying more starline brass.

If your dies are in a plate or not adjusted, I can see a scenario where the work hardened brass at the top part of the case has a different appearance than the rest of the case and is in fact smaller, because of the lack of sizing the rest of the case over multiple reloads.

Have you tried sizing with a different die, or see if a full length resize might help? I've used ACP dies when I had my Colt dies loaned out before, without problems.

HTH

Not sure if this is your case but I had a problem with RCBS dies that was strange. The Crimping die had the decapping pin in it and the sizing die had the seating stem in it. The sides of the die are labeled if you can read them. These were on a set of their Cowboy dies in 44-40. You may want to check and see if they were switched around at the factory as mine were.