If you're trying to thin the chunks down into a preform, the antler is the way to go. You don't need that unholy copper anyway, antler is better.
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If you're trying to knock spalls off the chunk to make small points from, a hammerstone is what you want, a big moose antler is good for spalling, but deer antler usually lacks the weight to knock off big spalls. Find a rounded hammerstone a little smaller than fist-sized, preferably a gritty river-smoothed stone that's hard enough to take the impact, but soft and gritty enough to "grab" the edge. Find an edge of your flint that's strong, but less than a 90 degree angle, and strike a glancing blow with the hammerstone, aiming for just a bit in from the edge. Let your swing follow through. You don't want to strike straight in, the glancing blow will take off a good spall if you get the angle right.
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