Hi Caperbound.
The first time I used an inertia bullet puller I had the shellholder upside down. (it was an older frankford arsenal but I think they are the same design. As a result, the case would move around and only after significant mashing and damage to the hammer rim and caseholder was I able to get the bullets out.
Here are a few things that have really worked for me.
1. Install the case holder the right side up.
2. Keep a few extra O-rings on hand because you can snap them when you are putting the caseholder over the belted rims.
3. I have found that the 'block of wood' as suggested just takes too long and has marginal results. I use a 25 lb cast steel weight that Ii use in my lead sled. Make sure your contact point on the lead is on a flat surface to avoid major splits on the hammer head.
4. On the first and second rasp of the hammer, just re tighten the shell holder screw top to make sure their is no play from the bullet case in the tool.
5. I have shoved some foam in the end of the hammer tool and tightly pack it before each pulling session so that I don't damage the bullet tip. This came in handy when I was unloading a few A-Max's and didn't deform one tip.
I have tried this method on heavily crimped and what appeared to be sealed and crimped factory ammunition with no issues. The solid steel has changed my life significantly for this process.
Best of luck, happy re-loading. If I can be of further help, please feel free to PM me.
Matt