The 0.357" is the measured outside diameter of the throat of the spent cases from my M48A; which should be the dimension of the chamber at the neck if I am thinking of this correctly. Then subtract twice the thickness of the brass at the case mouth, which is approximately 0.015" (measured) thick each side, to get 0.327" calculated. I then used digital calipers to measure the same dimension on about 15 more pieces of spent brass. I measured the same 0.327" inside of the mouth of the spent brass after removing any vestige of the crimp as well as I could. Now you have it.
My conclusion is that my M48A does not have the "loose" throat that I had been worried about. I also think, from the 3.22" OAL that I got from slugging the throat of the M48A (and confirmed through use of Forster Headspace gages) and the dimensions of the Karabiner and Maximum, that I should not have any trouble chambering and firing both of those boolits after sizing them down to 0.323". It has a normal throat. The excersize with determining the inside fired neck diameter is to tell you what size to size your bullet.... and that would be about 0.0005" under what you measured... or about 0.3265"
I am constantly amazed at how much individuals here and at Cast Boolits are willing to invest their time and knowledge to help individuals whom they have never met and have nothing to gain from. It says a lot about the community that frequents these venues and I thank you and Bruce a LOT for your help on this issue. I hope that posting all of this information will help others in their efforts to safely determine whether a new boolit design is suitable for use in their own weapons: as I have seen you try to warn others at Cast Boolits. Be carefull who you take advice from there, some have their own agenda to make them look good. Anyone who tells you you can't do something is passing along "Old Wives Tales".
There is a discussion of a boolit (the Cruise Missile) on Cast Boolits that will not chamber in some rifles because the molds are cut too large. The boolit was designed correctly. The specs for the boolit were given to the mold producer correctly. But the molds were cut oversized and will not chamber in some rifles in which they would chamber if the molds did not produce oversized boolits. Imagine how disappointed you would be if you received a mold that you had checked out and determined the boolit would chamber in your weapon but when you got the mold you could not cast anything that would chamber in your rifle/handgun? Happens quite a bit when Lee cuts the mold it seems.
I am not affiliated with either 45 2.1 or Bruce at BRP Products and have nothing to gain from this except two good looking boolits to feed my M48A. Bruce, at BRP, will not cut a mold so large that what it casts can not be chambered. 45 2.1 won't design a boolit like that or work with a machinist who will cut it oversized. They both have spent a rediculous amount of time with me teaching me about my own rifle for no reason except to help. That is the kind of person that I put my trust in when it comes time to part with money. Thanks for the plug."