I hate to admit this, BUT: I had a Zabala 3 1/2 10bore, I also had some 10-12 "lil Skeeters". I shot a 3 1/2 12 cartidge using that rig in the Zabala..No problem, except the plastic hull and the lil skeeter became one, amd still are..FYI there was no problem with the length of the insert, it was 3 /12