Thread: 44-40 Lee Size die issue for Pistol

I don't think it's the die it's the fact that the chamber they were last shot in is larger than the revolver cylinder chambers in the case head area of the brass the sizing die can't size that's below the top of the shell holder.

I would try popping the cases that are problematic into your shell holder and measure with a feeler gauge under them to figure out how much it takes to jam the rim to the top of the shell holder groove.
Take the decapping pin out of the die then size with either the feeler gauge or a shim of the same thickness. This might just get enough sized to work depending on how much slop is in the shell holder fit.

If not you could also try modifying the shell holder to be thinner so the die can come further down the brass. Do this by grinding down the top of the shell holder.

Just remember dies only return brass to spec in areas they can reach so brass will not always be interchangeable between guns if the chambers are different in the case head area as this area can't be resized (well it can be but isn't in a standard set up).