Running your bullets through a Lee .311" sizer will crimp the gas checks on. Even if the bullet is smaller than .311, the larger g.c. should cork things up. With the g.c. now assuredly staying with the bullet, hopefully things will improve.
I would also suggest positioning the 23/3031 to the back of the case for the best result. A 1" square of paper towel folded into a 1/2" square and placed on the top of the powder works well as does partially chambering a round then raising the muzzle momentarily and then closing the action when the muzzle is on the target.
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