I'd have to agree with jaydeee. The collet has to have at least a bit of something to hold onto. The RCBS collet puller works great when it's got a bit of meat to grab onto, but the shape of a semi-wad just isn't condusive to being grabbed and held.
One should also keep in mind that the RCBS collet/bullet puller die system doesn't work well with pure lead bullets. I've pulled some longer 30 cal with it, but you've got to really crank down on the handle. It just wouldn't grab 44 mag round nosers at all.