No need for one of those big, heavy(expensive) things and all. Here's a simple portable one that only requires a little cutting. Go to an Ace Hardware ,or local hardware, I went to Ace. Go to the tool section and look for a "fence post driver". It has two robust handles on it. Also find a long, heavy(16 pound) iron bar that has one end hammered flat to look like a chisle with 3 inch blade. The other end of the bar will have been flattened to look like the head of a nail. That is the part you want. Find the balance point of the bar and cut it. You now have a portable sample stamp. Invert the tube, put in a handfull of course material and use the nail end of the bar to quickly stamp it into pulverized rock. If I can find my digital, I'll take pics of mine. TTC