OP - keep in mind that bottlenecked rifle cases are tapered, and when fired they will expand in size a little. Some guns may have slightly larger chambers, and cases fired in them can be a tad larger. So, when you're resizing them, you're really having to force them back down to original dimensions, and that can be tough even when properly lubed. Full-auto weapons usually have slightly larger chambers, so brass ran through an MG can be a little tougher to resize.
Straight walled pistol brass doesn't need lubing with carbide resizing dies, but anything tapered definitely does! Even .30 Carbine. Stuck cases really make me hate life. Get a .30-06 stuck if you want a real good time.