When you get it, hammer a few clean nails into some scrap, flush with te surface and then try it out - to get the technique. Then do a few below the surface and try again ... easier to practice at ground level and perfect it.
Well the Priory Nail puller arrived. It works pretty good. I am cutting some material away from the nail to get the jaws in as the wood is really hard and the slide hammer isn't really getting in there. It certainly gets hold of the headless rusty stumps though and the leverage you get makes it easy to extract the nail, so thanks for the suggestion!
Must be very hard! Although from what you are saying it pull them out - a reasonable buy? If you cannot get teh jaws in, try turning through 90 degrees and see if you can get through teh grain that way.
Where it's not rotten, it is like iron (Its a 120 year old beam in the roof of our house). It's a lot easier to dig a small section of wood out each side of the nail stump than bash away at it with the slide. Once the jaws get onto a solid bit of the nail (not flakey rust) then it pulls them out perfectly!