I've used 7.62, 223, 45 colt, 45acp, .410 shot, 454, 40, 9, 30.06, 8mm mauser, etc etc. I do like spent .410 as a tamper, but those aren't the strangest, I've grabbed whatever is closest to me for tamping a lot which has led me to using markers, pens, drill bits, bones and ivory, batteries,(AA and AAA), leather working tools, nails screws and bolts, another pipe's stem, a stick, a rock, finger, antler, and my favorite emergency tamp....a rolled up pipe cleaner to create a "foot". If it fits, it tamps, I probably missed some.