OK - using that welded-in collar makes sense now for a BLOWBACK only. Gotcha!
I assume Mach3 is a CAD program of some sort? That would be cool! IF IT WERE ME, I'd make a raw bolt blank with a small diameter opening in the face so that I could build it into whatever sized face I need on the lathe at a later date.
Making my own bolts is on the menu. In fact it is one of the reasons I got the indexing head. I need more collets as it doesn't take the ones I have :( The challenge that I see is going to be drilling the small pin hole for the firing pin retainer in the hard steel. It is surely going to be a difficult task. The other things will be relatively simple tasks on the mill with a rotary table (or a lathe with a milling attachment). A slitting saw for the ejector groove. Then temper the metal to the approprate hardness for the metal in question. I have a big piece of 4340 steel but it is actually TOO BIG and I need to get a smaller piece LOL.
Wow as I'm typing this a deer just walked through the trees in my backyard! :)