Take any ten gauge barrel set, off the gun, with the extractors in the "in" position. A 12 gauge shell fits right in the chamber, a little deep, but not beyond the rim recess.
Ever run out of 10ga ammo or grab the wrong box on the way to the blind? A little tape wrapped around a 12 gauge shell to center it in the chamber and it will work fine in a 10ga. It will split every shell but it will still kill ducks dead.
jOey, you were wrong. It is obvious without pics. If you think you are some how making your point because no one will give in to your demand for pics, you are again, wrong.
PS Eightbore and I have never met, nor are we 'buddies', we just know a braggart and a bore when we see one.