I am trying to build a .410 shotgun, rifled slug gun using brass shells. To do this I am using 9.3x74R brass. I plan to trim to 2.5", and fire form. There is a number of sources on how to do this, however, my question pertains to the chamber.
I intend to shoot these hard, up to full power 45,000 psi levels. I plan to have a chamber reamer made, but it needs to be able to safely chamber and fire a .410 plastic shotgun shell to remain what is considered a shotgun by the DNR.
I'll post below what a Federal .410 plastic shotgun (labeld .410 shotgun) shell measures, followed by a 9.3x74R (labeled .410) sized approximately what it would measure for my purposes. My main concern is the case web, which measures .473" on a .410 plastic shell, and .463" on the 9.3x74R brass.
Now this will be built on a bolt action, and I do not ever intend on shooting plastic shells out of it besides just to test fire, or prove that it is a .410 shotgun to a DNR officer. Can I get away with a chamber that is .474" at the opening? If so, will .011" oversize cause any safety problems with 9.3x74R brass?