Ifa 12 gauge is choked or undersized, then many folks douse the smaller 13 gauge fiber wads or elsethe 12gaugewads may be tight at themuzzle.
Analternative is touse 2 of the more flexible 12 gauge wool wads, or toapply, soak or melt somelubricantontothe 12 gauge fiber wadsto better help them conform to the bore. Cutting 12 gauge fiber wads in half and/or cuttingsome grease grooves around their diametercan further helpto make their insertioneasier.Just fill the grooves with bore butter,others mightapply a little olive oil and let it soak in.