I am not sure what the material is, I just got them yesterday and did not have a lot of time to look at them. When I talked to the guy at RCBS he said it sounded like the stem was having a problem. They are going to send me a polished one to see if that helps.
I just can't say enough about customer service in the reloading industry, it seems that they remember more so than any other industry generally speaking, what good service means as well pride in workmanship and your job means.
* (Swinging club) Whack! whack! whack! *
Nope, the old nag's still dead .