You might want to try a black powder field shot wad inserted upside down over the shot instead of the wax. It would still compress properly going through the choke and hold the shot together better when it hits the gel block. I think you can get them at Ballistic products. Unlike a slug a wax slug goes through the choke like a solid piece of lead instead of the rifled slug which is designed to compress the rifling fins when it goers through the choke. Without the wax holding the shot together it can shift around when the shot wad gets compressed but should still retain its integrity once out of the bore.
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