Gaz, those nickel plated cases are still brass, and brass is, or course, the best. Steel rounds in revolvers can give problems in extraction since the steel doesn't spring back as well as brass.
The aluminum cases, which are only made by CCI and may not be available to you, are better than steel in my experience. But they still can be a little reluctant to fall out of the cylinder.
I may be imagining it, but it sometimes seems like a warmed-up revolver will have slower extractions than a cold one. I know that seems odd since it isn't much warming I'm talking about. And it may just be the chambers getting dirty.
There is such a thing as a chamber brush. It will look like a regular bore cleaning brush but have slightly larger diameter, to clean better where the brass sits in the chamber.
It may be that only one chamber in six is causing a problem, since it would hinder the ejection of all brass due to them all coming out at once. Perhaps if you concentrate on the worst looking one, you can get what you want with minimum effort.
“There’s a rattle in my glove box,
A Federal twelve-gauge slug.” – Adam Carroll in song Porter Wagoner