I have an interesting project I started that is giving me fits. I bought a 28 gauge rolling block shotgun and had it shipped directly to my gunsmith to be rifled to 1:66 He has done this with a 20 gauge for me once before with good results. The problem is the chamber. The base mics out at .660. 24 gauge brass is .658 at base. The chamber cast at the rifling is .645. The 24 gauge brass is close. but the brass will not chamber. I took a case and pounded it into the chamber until about .5 inch protruded. That is as far as it got. Knocked it out with a long dowel and the mouth of the case had shrunk to about .640. Maybe he cast has expanded since I made it. Still, about an hour with emory cloth and split dowel made no noticeable difference. How much do you think a smith would charge to polish this chamber out to take the brass. I suspect 28 gauge cases would be too smallm but do not have dimensions of either commercial plastic or Magtech brass cases. Can anyone provide those? Tanks!