I'm finding the chambers tight on the new to me 10 gauge. I've loaded mostly plastic hulls cut down from 3-1/2" magnum. The once fired hulls of course have been shot in different guns and were magnum loads. They haven't been a problem in my other 10 gauge - a Baker Syracuse. I've got a MEC 600 in 10 gauge and I have to make sure the brass is sized all the way to the rim. They fit fine and extract when so sized. I've not shot any newly loaded ammo.