Clamping feednecks work great, if you plan on using the same loader for different markers, or different loaders on the same marker. I keep a backup grav-feed, in case my ReloaderB takes a dump. I need the feedneck to be able to adapt.
But I have heard great things about the CP feedneck. Is your Halo sanded? not sanded? Just out of the box? If it's been sanded, use the small sleeve. If it's straight out of the box, use the medium. Large is for the Empire Reloader, but I can't see why it would be different. Same shells, but maybe they see a difference that I can't.
Four wheels move the body....
Two wheels move the soul.