Received the brass today and I do have bad news.
According to ANSI spec's the .223 REM. chamber headspace should measure from 1.4636" - 1.4736" a maximum of .0100" ten thousand of an inch difference. This is from the tables of my RCBS precision mic.
Yours measure .0180", .0180", .0200", .0200" and an oddball at .0060". If we throw out the oddball you have an average of .0190" or nineteen thousands of an inch after they cooled and shrunk. So if we add .0030" to that for shrinkage you are looking at .0220" twenty two thousands of an inch. more than double the maximum allowable.
As a reference I measured 10 pieces out of my Remington 700P and the average was -.0020" after cooling and shrinkage, so my actual headspace is .0010" where yours is .0220". My opinion would be that the rifle is dangerous to use as is whether as a bolt action or semi action. You have a very dangerous situation in you hands, a more powerful .223 round than you are using can have disastrous results.
Further visual observations show that all 5 pieces are at the edge of failure; severe thinning near the base, poorly fire formed and the only case that was .0060" had the primer popped out of it and severely bulged.
Best case the barrel might be salvageable, it needs the shoulder to be re-cut/set-back and the chamber cut to the correct headspace to match your bolt. The problem with that is it needs to be set-back by one thread pitch so the gas port is indexed correctly but that brings the gas port closer to the receiver and that may cause a problem with the op rod and closing of the bolt. Worse case you will need a new barrel.
Given that the mini's barrel is not a standard profile or configuration and not too many gunsmiths work with them you may have a problem finding one that will work on it. If you do, I don't imagine it will be cheap with either option.
I can't tell you what to do but if I were in your situation I would be sending it back to the seller. He sold you a problem that he created whether he knew it or not.
Keep in mind that this is my opinion and not of a gunsmith.
I have been around firearms for a very long time, reload and do all my repairs. I am a machinist so I do understand what it takes but that still does not make me a gunsmith.
