Did you reuse the same cases that you pulled the bullets from? If so, that could be your culprit. The neck tension on a case is loose once you pull a bullet. You can easily feel this when you seat a bullet into the case... it will seat really easy.
Other than that, the only thing you can do to a bullet to damage it with a kinetic puller is maybe deform the tip, but you would have had to damage it pretty bad in order to cause "horrible" groups.
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